diff --git a/.gitignore b/.gitignore
index 09dacbc..5243bad 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,5 @@
 prototype/chain-manager/patch.*
+.eqc-info
 .eunit
 deps
 *.plt
@@ -6,3 +7,6 @@ erl_crash.dump
 .concrete/DEV_MODE
 .rebar
 edoc
+
+# PB artifacts for Erlang
+include/machi_pb.hrl
diff --git a/Makefile b/Makefile
index a118de4..c273ed6 100644
--- a/Makefile
+++ b/Makefile
@@ -37,13 +37,18 @@ PLT = $(HOME)/.machi_dialyzer_plt
 build_plt: deps compile
 	dialyzer --build_plt --output_plt $(PLT) --apps $(APPS) deps/*/ebin
 
+DIALYZER_DEP_APPS = ebin/machi_pb.beam deps/protobuffs/ebin
+DIALYZER_FLAGS = -Wno_return -Wrace_conditions -Wunderspecs
+
 dialyzer: deps compile
-	dialyzer -Wno_return --plt $(PLT) ebin
+	dialyzer $(DIALYZER_FLAGS) --plt $(PLT) ebin $(DIALYZER_DEP_APPS) | \
+            egrep -v -f ./filter-dialyzer-dep-warnings
 
 dialyzer-test: deps compile
 	echo Force rebar to recompile .eunit dir w/o running tests > /dev/null
 	rebar skip_deps=true eunit suite=lamport_clock
-	dialyzer -Wno_return --plt $(PLT) .eunit
+	dialyzer $(DIALYZER_FLAGS) --plt $(PLT) .eunit $(DIALYZER_DEP_APPS) | \
+            egrep -v -f ./filter-dialyzer-dep-warnings
 
 clean_plt:
 	rm $(PLT)
diff --git a/filter-dialyzer-dep-warnings b/filter-dialyzer-dep-warnings
new file mode 100644
index 0000000..b71c024
--- /dev/null
+++ b/filter-dialyzer-dep-warnings
@@ -0,0 +1,12 @@
+####################### patterns for general errors in dep modules:
+^protobuffs\.erl:
+^protobuffs_[a-z_]*\.erl:
+^leexinc\.hrl:[0-9][0-9]*: 
+^machi_chain_manager1.erl:[0-9][0-9]*: Guard test RetrospectiveP::'false' =:= 'true' can never succeed
+^machi_pb\.erl:[0-9][0-9]*: 
+^pokemon_pb\.erl:[0-9][0-9]*: 
+####################### patterns for unknown functions:
+^  basho_bench_config:get/2
+^  erl_prettypr:format/1
+^  erl_syntax:form_list/1
+^  machi_partition_simulator:get/1
diff --git a/rebar b/rebar
index 146c9aa..d53a235 100755
Binary files a/rebar and b/rebar differ
diff --git a/rebar.config b/rebar.config
index 88f9c3d..bb37270 100644
--- a/rebar.config
+++ b/rebar.config
@@ -5,6 +5,7 @@
 {edoc_opts, [{dir, "./edoc"}]}.
 
 {deps, [
-        {lager, ".*", {git, "git://github.com/basho/lager.git", {tag, "2.0.1"}}}
+        {lager, ".*", {git, "git://github.com/basho/lager.git", {tag, "2.0.1"}}},
+        {protobuffs, "0.8.*", {git, "git://github.com/basho/erlang_protobuffs.git", {tag, "0.8.1p4"}}}
         ]}.
 
diff --git a/src/machi.proto b/src/machi.proto
new file mode 100644
index 0000000..993ff42
--- /dev/null
+++ b/src/machi.proto
@@ -0,0 +1,185 @@
+/* -------------------------------------------------------------------
+**
+** machi.proto: Protocol Buffers definition for Machi
+**
+** Copyright (c) 2014-2015 Basho Technologies, Inc.  All Rights Reserved.
+**
+** This file is provided to you under the Apache License,
+** Version 2.0 (the "License"); you may not use this file
+** except in compliance with the License.  You may obtain
+** a copy of the License at
+**
+**   http://www.apache.org/licenses/LICENSE-2.0
+**
+** Unless required by applicable law or agreed to in writing,
+** software distributed under the License is distributed on an
+** "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+** KIND, either express or implied.  See the License for the
+** specific language governing permissions and limitations
+** under the License.
+**
+** -------------------------------------------------------------------
+*/
+
+/*
+** Revision: 0.1
+*/
+
+// Java package specifiers
+option java_package = "com.basho.machi.protobuf";
+option java_outer_classname = "MachiPB";
+
+//////////////////////////////////////////
+//
+// enums
+//
+//////////////////////////////////////////
+
+enum Mpb_GeneralStatusCode {
+     OK = 0;
+     BAD_ARG = 1;
+     WEDGED = 2;
+     BAD_CHECKSUM = 3;
+     PARTITION = 4;
+}
+
+// Must match with machi.hrl's values!
+enum Mpb_CSumType {
+     CSUM_TAG_NONE = 0;
+     CSUM_TAG_CLIENT_GEN = 1;
+     CSUM_TAG_SERVER_GEN = 2;
+     CSUM_TAG_SERVER_REGEN = 3;
+}
+
+//////////////////////////////////////////
+//
+// basic data types
+//
+//////////////////////////////////////////
+
+// chunk_pos() type
+message Mpb_ChunkPos {
+    required uint64 offset = 1;
+    required uint64 chunk_size = 2;
+    required string file_name = 3;
+}
+
+// chunk_csum() type
+message Mpb_ChunkCSum {
+    required Mpb_CSumType type = 1;
+    required bytes csum = 2;
+}
+
+// epoch_id() type
+message Mpb_EpochId {
+    required uint32 epoch_num = 1;
+    required Mpb_ChunkCSum epoch_csum = 2;
+}
+
+//////////////////////////////////////////
+//
+// requests & responses
+//
+//////////////////////////////////////////
+
+// Error response - may be generated for any Req
+message Mpb_ErrorResp {
+    // Free-form (depends on server, which is probably a bad idea TODO)
+    required int32 code = 1;
+    required string msg = 2;
+    optional bytes extra = 3;
+}
+
+// ping() request & response
+
+message Mpb_EchoReq {
+    optional string message = 1;
+}
+
+message Mpb_EchoResp {
+    optional string message = 1;
+}
+
+// Authentication request & response
+
+message Mpb_AuthReq {
+    required bytes user = 1;
+    required bytes password = 2;
+}
+
+message Mpb_AuthResp {
+    required uint32 code = 1;
+    // TODO: not implemented yet
+}
+
+// append_chunk() request & response
+
+message Mpb_AppendChunkReq {
+    required string prefix = 1;
+    optional bytes placement_key = 2;
+    required bytes chunk = 3;
+    optional uint32 chunk_extra = 4;
+}
+
+message Mpb_AppendChunkResp {
+    required Mpb_GeneralStatusCode status = 1;
+    // If OK, then chunk_pos is defined.
+    optional Mpb_ChunkPos chunk_pos = 2;
+}
+
+// write_chunk() request & response
+
+message Mpb_WriteChunkReq {
+    required string file = 1;
+    required uint64 offset = 2;
+    required bytes chunk = 3;
+}
+
+message Mpb_WriteChunkResp {
+    required Mpb_GeneralStatusCode status = 1;
+    // If OK, then chunk_pos is defined.
+    optional Mpb_ChunkPos chunk_pos = 2;
+}
+
+//////////////////////////////////////////
+//
+// request & response wrapper
+//
+//////////////////////////////////////////
+
+message Mpb_Request {
+    // TODO: If we wish to support pipelined requests sometime in the
+    // future, this is the placeholder to do it.
+    required bytes req_id = 1;
+
+    // The client should only define one request message.  If the client
+    // includes multiple requests here, the server may pick/choose an
+    // arbitrary one.
+    // NOTE: The erlang protobuffs compiler doesn't support 'oneof'.
+    //       But 'oneof' appears to be a very tiny memory optimization
+    //       that not all languages might care about?  (Erlang doesn't)
+    optional Mpb_EchoReq echo = 10;
+    optional Mpb_AuthReq auth = 11;
+    optional Mpb_AppendChunkReq append_chunk = 12;
+    optional Mpb_WriteChunkReq write_chunk = 13;
+}
+
+message Mpb_Response {
+    // TODO: If we wish to support pipelined requests sometime in the
+    // future, this is the placeholder to do it.
+    required bytes req_id = 1;
+
+    // The server will define only one of the optional responses below.
+
+    // Generic error response, typically used when something quite
+    // bad/unexpected happened within the server.
+    // Clients should always check this response and, if defined,
+    // ignroe any request-specific response at codes 10+.
+    optional Mpb_ErrorResp generic = 2;
+
+    // Specific responses.
+    optional Mpb_EchoResp echo = 10;
+    optional Mpb_AuthResp auth = 11;
+    optional Mpb_AppendChunkResp append_chunk = 12;
+    optional Mpb_WriteChunkResp write_chunk = 13;
+}
diff --git a/src/machi_admin_util.erl b/src/machi_admin_util.erl
index 207adf9..f5702c2 100644
--- a/src/machi_admin_util.erl
+++ b/src/machi_admin_util.erl
@@ -22,10 +22,6 @@
 
 -module(machi_admin_util).
 
-%% TODO Move these types to a common header file? (also machi_flu1_client.erl?)
--type inet_host()   :: inet:ip_address() | inet:hostname().
--type inet_port()   :: inet:port_number().
-
 -export([
          verify_file_checksums_local/3,  verify_file_checksums_local/4,
          verify_file_checksums_remote/3, verify_file_checksums_remote/4
@@ -37,13 +33,13 @@
 
 -define(FLU_C, machi_flu1_client).
 
--spec verify_file_checksums_local(port(), machi_flu1_client:epoch_id(), binary()|list()) ->
+-spec verify_file_checksums_local(port(), machi_dt:epoch_id(), binary()|list()) ->
       {ok, [tuple()]} | {error, term()}.
 verify_file_checksums_local(Sock1, EpochID, Path) when is_port(Sock1) ->
     verify_file_checksums_local2(Sock1, EpochID, Path).
 
--spec verify_file_checksums_local(inet_host(), inet_port(),
-                                  machi_flu1_client:epoch_id(), binary()|list()) ->
+-spec verify_file_checksums_local(machi_dt:inet_host(), machi_dt:inet_port(),
+                                  machi_dt:epoch_id(), binary()|list()) ->
       {ok, [tuple()]} | {error, term()}.
 verify_file_checksums_local(Host, TcpPort, EpochID, Path) ->
     Sock1 = ?FLU_C:connect(#p_srvr{address=Host, port=TcpPort}),
@@ -53,13 +49,13 @@ verify_file_checksums_local(Host, TcpPort, EpochID, Path) ->
         catch ?FLU_C:disconnect(Sock1)
     end.
 
--spec verify_file_checksums_remote(port(), machi_flu1_client:epoch_id(), binary()|list()) ->
+-spec verify_file_checksums_remote(port(), machi_dt:epoch_id(), binary()|list()) ->
       {ok, [tuple()]} | {error, term()}.
 verify_file_checksums_remote(Sock1, EpochID, File) when is_port(Sock1) ->
     verify_file_checksums_remote2(Sock1, EpochID, File).
 
--spec verify_file_checksums_remote(inet_host(), inet_port(),
-                                   machi_flu1_client:epoch_id(), binary()|list()) ->
+-spec verify_file_checksums_remote(machi_dt:inet_host(), machi_dt:inet_port(),
+                                   machi_dt:epoch_id(), binary()|list()) ->
       {ok, [tuple()]} | {error, term()}.
 verify_file_checksums_remote(Host, TcpPort, EpochID, File) ->
     Sock1 = ?FLU_C:connect(#p_srvr{address=Host, port=TcpPort}),
diff --git a/src/machi_basho_bench_driver.erl b/src/machi_basho_bench_driver.erl
index 090f3a6..6fd4b59 100644
--- a/src/machi_basho_bench_driver.erl
+++ b/src/machi_basho_bench_driver.erl
@@ -26,7 +26,7 @@
 %% use basho_bench to measure its performance under a certain
 %% workload.  Machi is a bit different than most KV stores in that the
 %% client has no direct control over the keys -- Machi servers always
-%% assign the keys.  The schemes typically used by basho_bench & YCSB
+%% assign the keys.  The schemes typically used by basho_bench & YCSB
 %% to use/mimic key naming conventions used internally ... are
 %% difficult to adapt to Machi.
 %%
@@ -50,7 +50,7 @@
 %%
 %% TODO: As an alternate idea, if we know that the chunks written are
 %% always the same size, and if we don't care about CRC checking, then
-%% all we need to know are the file names & file sizes on the server:
+%% all we need to know are the file names & file sizes on the server:
 %% we can then pick any valid offset within that file.  That would
 %% certainly be more scalable than the zillion-row-ETS-table, which is
 %% definitely RAM-hungry.
@@ -67,9 +67,9 @@
 -define(ETS_TAB, machi_keys).
 -define(THE_TIMEOUT, 60*1000).
 
--define(INFO(Str, Args), lager:info(Str, Args)).
--define(WARN(Str, Args), lager:warning(Str, Args)).
--define(ERROR(Str, Args), lager:error(Str, Args)).
+-define(INFO(Str, Args), (_ = lager:info(Str, Args))).
+-define(WARN(Str, Args), (_ = lager:warning(Str, Args))).
+-define(ERROR(Str, Args), (_ = lager:error(Str, Args))).
 
 new(Id) ->
     Ps = find_server_info(Id),
diff --git a/src/machi_cr_client.erl b/src/machi_cr_client.erl
index ac7134b..09ef18d 100644
--- a/src/machi_cr_client.erl
+++ b/src/machi_cr_client.erl
@@ -119,6 +119,7 @@
          %% File API
          append_chunk/3, append_chunk/4,
          append_chunk_extra/4, append_chunk_extra/5,
+         write_chunk/4, write_chunk/5,
          read_chunk/4, read_chunk/5,
          checksum_list/2, checksum_list/3,
          list_files/1, list_files/2,
@@ -180,6 +181,19 @@ append_chunk_extra(PidSpec, Prefix, Chunk, ChunkExtra, Timeout) ->
                                     Chunk, ChunkExtra}},
                     Timeout).
 
+%% @doc Write a chunk of data (that has already been
+%% allocated/sequenced by an earlier append_chunk_extra() call) to
+%% `File' at `Offset'.
+
+write_chunk(PidSpec, File, Offset, Chunk) ->
+    write_chunk(PidSpec, File, Offset, Chunk, ?DEFAULT_TIMEOUT).
+
+%% @doc Read a chunk of data of size `Size' from `File' at `Offset'.
+
+write_chunk(PidSpec, File, Offset, Chunk, Timeout) ->
+    gen_server:call(PidSpec, {req, {write_chunk, File, Offset, Chunk}},
+                    Timeout).
+
 %% @doc Read a chunk of data of size `Size' from `File' at `Offset'.
 
 read_chunk(PidSpec, File, Offset, Size) ->
@@ -252,6 +266,8 @@ code_change(_OldVsn, S, _Extra) ->
 
 handle_call2({append_chunk_extra, Prefix, Chunk, ChunkExtra}, _From, S) ->
     do_append_head(Prefix, Chunk, ChunkExtra, 0, os:timestamp(), S);
+handle_call2({write_chunk, File, Offset, Chunk}, _From, S) ->
+    do_write_head(File, Offset, Chunk, 0, os:timestamp(), S);
 handle_call2({read_chunk, File, Offset, Size}, _From, S) ->
     do_read_chunk(File, Offset, Size, 0, os:timestamp(), S);
 handle_call2({checksum_list, File}, _From, S) ->
@@ -338,8 +354,13 @@ do_append_midtail(_RestFLUs, Prefix, File, Offset, Chunk, ChunkExtra,
                             %% over with a new sequencer assignment, at
                             %% the 2nd have of the impl (we have already
                             %% slept & refreshed the projection).
-                            do_append_head2(Prefix, Chunk, ChunkExtra, Depth,
-                                            STime, S2);
+
+                            if Prefix == undefined -> % atom! not binary()!!
+                                    {error, partition};
+                               true ->
+                                    do_append_head2(Prefix, Chunk, ChunkExtra,
+                                                    Depth, STime, S2)
+                            end;
                         RestFLUs3 ->
                             do_append_midtail2(RestFLUs3, Prefix, File, Offset,
                                                Chunk, ChunkExtra,
@@ -378,6 +399,51 @@ do_append_midtail2([FLU|RestFLUs]=FLUs, Prefix, File, Offset, Chunk,
             exit({todo_should_never_happen,?MODULE,?LINE,File,Offset})
     end.
 
+do_write_head(File, Offset, Chunk, 0=Depth, STime, S) ->
+    do_write_head2(File, Offset, Chunk, Depth + 1, STime, S);
+do_write_head(File, Offset, Chunk, Depth, STime, #state{proj=P}=S) ->
+    %% io:format(user, "head sleep1,", []),
+    sleep_a_while(Depth),
+    DiffMs = timer:now_diff(os:timestamp(), STime) div 1000,
+    if DiffMs > ?MAX_RUNTIME ->
+            {reply, {error, partition}, S};
+       true ->
+            %% This is suboptimal for performance: there are some paths
+            %% through this point where our current projection is good
+            %% enough.  But we're going to try to keep the code as simple
+            %% as we can for now.
+            S2 = update_proj(S#state{proj=undefined, bad_proj=P}),
+            case S2#state.proj of
+                P2 when P2 == undefined orelse
+                        P2#projection_v1.upi == [] ->
+                    do_write_head(File, Offset, Chunk, Depth + 1, STime, S2);
+                _ ->
+                    do_write_head2(File, Offset, Chunk, Depth + 1, STime, S2)
+            end
+    end.
+
+do_write_head2(File, Offset, Chunk, Depth, STime,
+               #state{epoch_id=EpochID, proj=P, proxies_dict=PD}=S) ->
+    [HeadFLU|RestFLUs] = mutation_flus(P),
+    Proxy = orddict:fetch(HeadFLU, PD),
+    case ?FLU_PC:write_chunk(Proxy, EpochID, File, Offset, Chunk, ?TIMEOUT) of
+        ok ->
+            %% From this point onward, we use the same code & logic path as
+            %% append does.
+            do_append_midtail(RestFLUs, undefined, File, Offset, Chunk,
+                              undefined, [HeadFLU], 0, STime, S);
+        {error, bad_checksum}=BadCS ->
+            {reply, BadCS, S};
+        {error, Retry}
+          when Retry == partition; Retry == bad_epoch; Retry == wedged ->
+            do_write_head(File, Offset, Chunk, Depth, STime, S);
+        {error, written}=Err ->
+            Err;
+        {error, not_written} ->
+            exit({todo_should_never_happen,?MODULE,?LINE,
+                  iolist_size(Chunk)})
+    end.
+
 do_read_chunk(File, Offset, Size, 0=Depth, STime,
               #state{proj=#projection_v1{upi=[_|_]}}=S) -> % UPI is non-empty
     do_read_chunk2(File, Offset, Size, Depth + 1, STime, S);
diff --git a/src/machi_dt.erl b/src/machi_dt.erl
new file mode 100644
index 0000000..6d94e6d
--- /dev/null
+++ b/src/machi_dt.erl
@@ -0,0 +1,70 @@
+%% -------------------------------------------------------------------
+%%
+%% Copyright (c) 2007-2015 Basho Technologies, Inc.  All Rights Reserved.
+%%
+%% This file is provided to you under the Apache License,
+%% Version 2.0 (the "License"); you may not use this file
+%% except in compliance with the License.  You may obtain
+%% a copy of the License at
+%%
+%%   http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing,
+%% software distributed under the License is distributed on an
+%% "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+%% KIND, either express or implied.  See the License for the
+%% specific language governing permissions and limitations
+%% under the License.
+%%
+%% -------------------------------------------------------------------
+
+-module(machi_dt).
+
+-include("machi_projection.hrl").
+
+-type chunk()       :: chunk_bin() | {chunk_csum(), chunk_bin()}.
+-type chunk_bin()   :: binary() | iolist().    % client can use either
+-type chunk_csum()  :: binary().               % 1 byte tag, N-1 bytes checksum
+-type chunk_summary() :: {file_offset(), chunk_size(), binary()}.
+-type chunk_s()     :: binary().               % server always uses binary()
+-type chunk_pos()   :: {file_offset(), chunk_size(), file_name_s()}.
+-type chunk_size()  :: non_neg_integer().
+-type error_general() :: 'bad_arg' | 'wedged' | 'bad_checksum'.
+-type epoch_csum()  :: binary().
+-type epoch_num()   :: -1 | non_neg_integer().
+-type epoch_id()    :: {epoch_num(), epoch_csum()}.
+-type file_info()   :: {file_size(), file_name_s()}.
+-type file_name()   :: float().%%%binary() | list().
+-type file_name_s() :: binary().                % server reply
+-type file_offset() :: non_neg_integer().
+-type file_size()   :: non_neg_integer().
+-type file_prefix() :: binary() | list().
+-type inet_host()   :: inet:ip_address() | inet:hostname().
+-type inet_port()   :: inet:port_number().
+-type projection()      :: #projection_v1{}.
+-type projection_type() :: 'public' | 'private'.
+
+-export_type([
+              chunk/0,
+              chunk_bin/0,
+              chunk_csum/0,
+              chunk_summary/0,
+              chunk_s/0,
+              chunk_pos/0,
+              chunk_size/0,
+              error_general/0,
+              epoch_csum/0,
+              epoch_num/0,
+              epoch_id/0,
+              file_info/0,
+              file_name/0,
+              file_name_s/0,
+              file_offset/0,
+              file_size/0,
+              file_prefix/0,
+              inet_host/0,
+              inet_port/0,
+              projection/0,
+              projection_type/0
+             ]).
+
diff --git a/src/machi_flu1.erl b/src/machi_flu1.erl
index 95424a0..af507c2 100644
--- a/src/machi_flu1.erl
+++ b/src/machi_flu1.erl
@@ -75,6 +75,7 @@
 -include_lib("kernel/include/file.hrl").
 
 -include("machi.hrl").
+-include("machi_pb.hrl").
 -include("machi_projection.hrl").
 
 -define(SERVER_CMD_READ_TIMEOUT, 600*1000).
@@ -91,7 +92,7 @@
           data_dir        :: string(),
           wedged = true   :: boolean(),
           etstab          :: ets:tid(),
-          epoch_id        :: 'undefined' | pv1_epoch(),
+          epoch_id        :: 'undefined' | machi_dt:epoch_id(),
           dbg_props = []  :: list(), % proplist
           props = []      :: list()  % proplist
          }).
@@ -343,6 +344,10 @@ net_server_loop(Sock, #state{flu_name=FluName, data_dir=DataDir}=S) ->
                     http_server_hack(FluName, PutLine, Sock, S);
                 <<"GET ", _/binary>>=PutLine ->
                     http_server_hack(FluName, PutLine, Sock, S);
+                <<"PROTOCOL-BUFFERS\n">> ->
+                    ok = gen_tcp:send(Sock, <<"OK\n">>),
+                    ok = inet:setopts(Sock, [{packet, 4}]),
+                    protocol_buffers_loop(Sock, S);
                 _ ->
                     machi_util:verb("Else Got: ~p\n", [Line]),
                     io:format(user, "TODO: Else Got: ~p\n", [Line]),
@@ -1009,6 +1014,20 @@ http_harvest_headers({ok, Hdr}, Sock, Acc) ->
     http_harvest_headers(gen_tcp:recv(Sock, 0, ?SERVER_CMD_READ_TIMEOUT),
                          Sock, [Hdr|Acc]).
 
+protocol_buffers_loop(Sock, S) ->
+    case gen_tcp:recv(Sock, 0) of
+        {ok, _Bin} ->
+            R = #mpb_response{req_id= <<"not paying any attention">>,
+                              generic=#mpb_errorresp{code=-6,
+                                                     msg="not implemented"}},
+            Resp = machi_pb:encode_mpb_response(R),
+            ok = gen_tcp:send(Sock, Resp),
+            protocol_buffers_loop(Sock, S);
+        {error, _} ->
+            (catch gen_tcp:close(Sock)),
+            exit(normal)
+    end.
+
 digest_header_goop([], G) ->
     G;
 digest_header_goop([{http_header, _, 'Content-Length', _, Str}|T], G) ->
diff --git a/src/machi_flu1_client.erl b/src/machi_flu1_client.erl
index da4a293..c19a36a 100644
--- a/src/machi_flu1_client.erl
+++ b/src/machi_flu1_client.erl
@@ -85,47 +85,22 @@
          trunc_hack/3, trunc_hack/4
         ]).
 
-%% TODO: Hrm, this kind of API use ... is it a bad idea?  We really want to
-%% encourage client-side checksums; thus it ought to be dead easy.
--type chunk()       :: chunk_bin() | {chunk_csum(), chunk_bin()}.
--type chunk_bin()   :: binary() | iolist().    % client can use either
--type chunk_csum()  :: binary().               % 1 byte tag, N-1 bytes checksum
--type chunk_summary() :: {file_offset(), chunk_size(), binary()}.
--type chunk_s()     :: binary().               % server always uses binary()
--type chunk_pos()   :: {file_offset(), chunk_size(), file_name_s()}.
--type chunk_size()  :: non_neg_integer().
--type error_general() :: 'bad_arg' | 'wedged' | 'bad_checksum'.
--type epoch_csum()  :: binary().
--type epoch_num()   :: -1 | non_neg_integer().
--type epoch_id()    :: {epoch_num(), epoch_csum()}.
--type file_info()   :: {file_size(), file_name_s()}.
--type file_name()   :: binary() | list().
--type file_name_s() :: binary().                % server reply
--type file_offset() :: non_neg_integer().
--type file_size()   :: non_neg_integer().
--type file_prefix() :: binary() | list().
--type inet_host()   :: inet:ip_address() | inet:hostname().
--type inet_port()   :: inet:port_number().
 -type port_wrap()   :: {w,atom(),term()}.
--type projection()      :: #projection_v1{}.
--type projection_type() :: 'public' | 'private'.
-
--export_type([epoch_id/0]).
 
 %% @doc Append a chunk (binary- or iolist-style) of data to a file
 %% with `Prefix'.
 
--spec append_chunk(port_wrap(), epoch_id(), file_prefix(), chunk()) ->
-      {ok, chunk_pos()} | {error, error_general()} | {error, term()}.
+-spec append_chunk(port_wrap(), machi_dt:epoch_id(), machi_dt:file_prefix(), machi_dt:chunk()) ->
+      {ok, machi_dt:chunk_pos()} | {error, machi_dt:error_general()} | {error, term()}.
 append_chunk(Sock, EpochID, Prefix, Chunk) ->
     append_chunk2(Sock, EpochID, Prefix, Chunk, 0).
 
 %% @doc Append a chunk (binary- or iolist-style) of data to a file
 %% with `Prefix'.
 
--spec append_chunk(inet_host(), inet_port(),
-                   epoch_id(), file_prefix(), chunk()) ->
-      {ok, chunk_pos()} | {error, error_general()} | {error, term()}.
+-spec append_chunk(machi_dt:inet_host(), machi_dt:inet_port(),
+                   machi_dt:epoch_id(), machi_dt:file_prefix(), machi_dt:chunk()) ->
+      {ok, machi_dt:chunk_pos()} | {error, machi_dt:error_general()} | {error, term()}.
 append_chunk(Host, TcpPort, EpochID, Prefix, Chunk) ->
     Sock = connect(#p_srvr{proto_mod=?MODULE, address=Host, port=TcpPort}),
     try
@@ -142,8 +117,8 @@ append_chunk(Host, TcpPort, EpochID, Prefix, Chunk) ->
 %% be reserved by the file sequencer for later write(s) by the
 %% `write_chunk()' API.
 
--spec append_chunk_extra(port_wrap(), epoch_id(), file_prefix(), chunk(), chunk_size()) ->
-      {ok, chunk_pos()} | {error, error_general()} | {error, term()}.
+-spec append_chunk_extra(port_wrap(), machi_dt:epoch_id(), machi_dt:file_prefix(), machi_dt:chunk(), machi_dt:chunk_size()) ->
+      {ok, machi_dt:chunk_pos()} | {error, machi_dt:error_general()} | {error, term()}.
 append_chunk_extra(Sock, EpochID, Prefix, Chunk, ChunkExtra)
   when is_integer(ChunkExtra), ChunkExtra >= 0 ->
     append_chunk2(Sock, EpochID, Prefix, Chunk, ChunkExtra).
@@ -156,9 +131,9 @@ append_chunk_extra(Sock, EpochID, Prefix, Chunk, ChunkExtra)
 %% be reserved by the file sequencer for later write(s) by the
 %% `write_chunk()' API.
 
--spec append_chunk_extra(inet_host(), inet_port(),
-                   epoch_id(), file_prefix(), chunk(), chunk_size()) ->
-      {ok, chunk_pos()} | {error, error_general()} | {error, term()}.
+-spec append_chunk_extra(machi_dt:inet_host(), machi_dt:inet_port(),
+               machi_dt:epoch_id(), machi_dt:file_prefix(), machi_dt:chunk(), machi_dt:chunk_size()) ->
+      {ok, machi_dt:chunk_pos()} | {error, machi_dt:error_general()} | {error, term()}.
 append_chunk_extra(Host, TcpPort, EpochID, Prefix, Chunk, ChunkExtra)
   when is_integer(ChunkExtra), ChunkExtra >= 0 ->
     Sock = connect(#p_srvr{proto_mod=?MODULE, address=Host, port=TcpPort}),
@@ -170,9 +145,9 @@ append_chunk_extra(Host, TcpPort, EpochID, Prefix, Chunk, ChunkExtra)
 
 %% @doc Read a chunk of data of size `Size' from `File' at `Offset'.
 
--spec read_chunk(port_wrap(), epoch_id(), file_name(), file_offset(), chunk_size()) ->
-      {ok, chunk_s()} |
-      {error, error_general() | 'not_written' | 'partial_read'} |
+-spec read_chunk(port_wrap(), machi_dt:epoch_id(), machi_dt:file_name(), machi_dt:file_offset(), machi_dt:chunk_size()) ->
+      {ok, machi_dt:chunk_s()} |
+      {error, machi_dt:error_general() | 'not_written' | 'partial_read'} |
       {error, term()}.
 read_chunk(Sock, EpochID, File, Offset, Size)
   when Offset >= ?MINIMUM_OFFSET, Size >= 0 ->
@@ -180,10 +155,10 @@ read_chunk(Sock, EpochID, File, Offset, Size)
 
 %% @doc Read a chunk of data of size `Size' from `File' at `Offset'.
 
--spec read_chunk(inet_host(), inet_port(), epoch_id(),
-                 file_name(), file_offset(), chunk_size()) ->
-      {ok, chunk_s()} |
-      {error, error_general() | 'not_written' | 'partial_read'} |
+-spec read_chunk(machi_dt:inet_host(), machi_dt:inet_port(), machi_dt:epoch_id(),
+                 machi_dt:file_name(), machi_dt:file_offset(), machi_dt:chunk_size()) ->
+      {ok, machi_dt:chunk_s()} |
+      {error, machi_dt:error_general() | 'not_written' | 'partial_read'} |
       {error, term()}.
 read_chunk(Host, TcpPort, EpochID, File, Offset, Size)
   when Offset >= ?MINIMUM_OFFSET, Size >= 0 ->
@@ -196,18 +171,18 @@ read_chunk(Host, TcpPort, EpochID, File, Offset, Size)
 
 %% @doc Fetch the list of chunk checksums for `File'.
 
--spec checksum_list(port_wrap(), epoch_id(), file_name()) ->
-      {ok, [chunk_summary()]} |
-      {error, error_general() | 'no_such_file' | 'partial_read'} |
+-spec checksum_list(port_wrap(), machi_dt:epoch_id(), machi_dt:file_name()) ->
+      {ok, [machi_dt:chunk_summary()]} |
+      {error, machi_dt:error_general() | 'no_such_file' | 'partial_read'} |
       {error, term()}.
 checksum_list(Sock, EpochID, File) ->
     checksum_list2(Sock, EpochID, File).
 
 %% @doc Fetch the list of chunk checksums for `File'.
 
--spec checksum_list(inet_host(), inet_port(), epoch_id(), file_name()) ->
-      {ok, [chunk_summary()]} |
-      {error, error_general() | 'no_such_file'} | {error, term()}.
+-spec checksum_list(machi_dt:inet_host(), machi_dt:inet_port(), machi_dt:epoch_id(), machi_dt:file_name()) ->
+      {ok, [machi_dt:chunk_summary()]} |
+      {error, machi_dt:error_general() | 'no_such_file'} | {error, term()}.
 checksum_list(Host, TcpPort, EpochID, File) when is_integer(TcpPort) ->
     Sock = connect(#p_srvr{proto_mod=?MODULE, address=Host, port=TcpPort}),
     try
@@ -218,15 +193,15 @@ checksum_list(Host, TcpPort, EpochID, File) when is_integer(TcpPort) ->
 
 %% @doc Fetch the list of all files on the remote FLU.
 
--spec list_files(port_wrap(), epoch_id()) ->
-      {ok, [file_info()]} | {error, term()}.
+-spec list_files(port_wrap(), machi_dt:epoch_id()) ->
+      {ok, [machi_dt:file_info()]} | {error, term()}.
 list_files(Sock, EpochID) ->
     list2(Sock, EpochID).
 
 %% @doc Fetch the list of all files on the remote FLU.
 
--spec list_files(inet_host(), inet_port(), epoch_id()) ->
-      {ok, [file_info()]} | {error, term()}.
+-spec list_files(machi_dt:inet_host(), machi_dt:inet_port(), machi_dt:epoch_id()) ->
+      {ok, [machi_dt:file_info()]} | {error, term()}.
 list_files(Host, TcpPort, EpochID) when is_integer(TcpPort) ->
     Sock = connect(#p_srvr{proto_mod=?MODULE, address=Host, port=TcpPort}),
     try
@@ -238,15 +213,15 @@ list_files(Host, TcpPort, EpochID) when is_integer(TcpPort) ->
 %% @doc Fetch the wedge status from the remote FLU.
 
 -spec wedge_status(port_wrap()) ->
-      {ok, {boolean(), pv1_epoch()}} | {error, term()}.
+      {ok, {boolean(), machi_dt:epoch_id()}} | {error, term()}.
 
 wedge_status(Sock) ->
     wedge_status2(Sock).
 
 %% @doc Fetch the wedge status from the remote FLU.
 
--spec wedge_status(inet_host(), inet_port()) ->
-      {ok, {boolean(), pv1_epoch()}} | {error, term()}.
+-spec wedge_status(machi_dt:inet_host(), machi_dt:inet_port()) ->
+      {ok, {boolean(), machi_dt:epoch_id()}} | {error, term()}.
 wedge_status(Host, TcpPort) when is_integer(TcpPort) ->
     Sock = connect(#p_srvr{proto_mod=?MODULE, address=Host, port=TcpPort}),
     try
@@ -257,16 +232,16 @@ wedge_status(Host, TcpPort) when is_integer(TcpPort) ->
 
 %% @doc Get the latest epoch number + checksum from the FLU's projection store.
 
--spec get_latest_epochid(port_wrap(), projection_type()) ->
-      {ok, epoch_id()} | {error, term()}.
+-spec get_latest_epochid(port_wrap(), machi_dt:projection_type()) ->
+      {ok, machi_dt:epoch_id()} | {error, term()}.
 get_latest_epochid(Sock, ProjType)
   when ProjType == 'public' orelse ProjType == 'private' ->
     get_latest_epochid2(Sock, ProjType).
 
 %% @doc Get the latest epoch number + checksum from the FLU's projection store.
 
--spec get_latest_epochid(inet_host(), inet_port(), projection_type()) ->
-      {ok, epoch_id()} | {error, term()}.
+-spec get_latest_epochid(machi_dt:inet_host(), machi_dt:inet_port(), machi_dt:projection_type()) ->
+      {ok, machi_dt:epoch_id()} | {error, term()}.
 get_latest_epochid(Host, TcpPort, ProjType)
   when ProjType == 'public' orelse ProjType == 'private' ->
     Sock = connect(#p_srvr{proto_mod=?MODULE, address=Host, port=TcpPort}),
@@ -278,17 +253,17 @@ get_latest_epochid(Host, TcpPort, ProjType)
 
 %% @doc Get the latest projection from the FLU's projection store for `ProjType'
 
--spec read_latest_projection(port_wrap(), projection_type()) ->
-      {ok, projection()} | {error, not_written} | {error, term()}.
+-spec read_latest_projection(port_wrap(), machi_dt:projection_type()) ->
+      {ok, machi_dt:projection()} | {error, not_written} | {error, term()}.
 read_latest_projection(Sock, ProjType)
   when ProjType == 'public' orelse ProjType == 'private' ->
     read_latest_projection2(Sock, ProjType).
 
 %% @doc Get the latest projection from the FLU's projection store for `ProjType'
 
--spec read_latest_projection(inet_host(), inet_port(),
-                       projection_type()) ->
-      {ok, projection()} | {error, not_written} | {error, term()}.
+-spec read_latest_projection(machi_dt:inet_host(), machi_dt:inet_port(),
+                             machi_dt:projection_type()) ->
+      {ok, machi_dt:projection()} | {error, not_written} | {error, term()}.
 read_latest_projection(Host, TcpPort, ProjType)
   when ProjType == 'public' orelse ProjType == 'private' ->
     Sock = connect(#p_srvr{proto_mod=?MODULE, address=Host, port=TcpPort}),
@@ -300,17 +275,17 @@ read_latest_projection(Host, TcpPort, ProjType)
 
 %% @doc Read a projection `Proj' of type `ProjType'.
 
--spec read_projection(port_wrap(), projection_type(), epoch_num()) ->
-      {ok, projection()} | {error, not_written} | {error, term()}.
+-spec read_projection(port_wrap(), machi_dt:projection_type(), machi_dt:epoch_num()) ->
+      {ok, machi_dt:projection()} | {error, not_written} | {error, term()}.
 read_projection(Sock, ProjType, Epoch)
   when ProjType == 'public' orelse ProjType == 'private' ->
     read_projection2(Sock, ProjType, Epoch).
 
 %% @doc Read a projection `Proj' of type `ProjType'.
 
--spec read_projection(inet_host(), inet_port(),
-                       projection_type(), epoch_num()) ->
-      {ok, projection()} | {error, not_written} | {error, term()}.
+-spec read_projection(machi_dt:inet_host(), machi_dt:inet_port(),
+                      machi_dt:projection_type(), machi_dt:epoch_num()) ->
+      {ok, machi_dt:projection()} | {error, not_written} | {error, term()}.
 read_projection(Host, TcpPort, ProjType, Epoch)
   when ProjType == 'public' orelse ProjType == 'private' ->
     Sock = connect(#p_srvr{proto_mod=?MODULE, address=Host, port=TcpPort}),
@@ -322,7 +297,7 @@ read_projection(Host, TcpPort, ProjType, Epoch)
 
 %% @doc Write a projection `Proj' of type `ProjType'.
 
--spec write_projection(port_wrap(), projection_type(), projection()) ->
+-spec write_projection(port_wrap(), machi_dt:projection_type(), machi_dt:projection()) ->
       'ok' | {error, 'written'} | {error, term()}.
 write_projection(Sock, ProjType, Proj)
   when ProjType == 'public' orelse ProjType == 'private',
@@ -331,8 +306,8 @@ write_projection(Sock, ProjType, Proj)
 
 %% @doc Write a projection `Proj' of type `ProjType'.
 
--spec write_projection(inet_host(), inet_port(),
-                       projection_type(), projection()) ->
+-spec write_projection(machi_dt:inet_host(), machi_dt:inet_port(),
+                       machi_dt:projection_type(), machi_dt:projection()) ->
       'ok' | {error, 'written'} | {error, term()}.
 write_projection(Host, TcpPort, ProjType, Proj)
   when ProjType == 'public' orelse ProjType == 'private',
@@ -346,17 +321,16 @@ write_projection(Host, TcpPort, ProjType, Proj)
 
 %% @doc Get all projections from the FLU's projection store.
 
--spec get_all_projections(port_wrap(), projection_type()) ->
-      {ok, [projection()]} | {error, term()}.
+-spec get_all_projections(port_wrap(), machi_dt:projection_type()) ->
+      {ok, [machi_dt:projection()]} | {error, term()}.
 get_all_projections(Sock, ProjType)
   when ProjType == 'public' orelse ProjType == 'private' ->
     get_all_projections2(Sock, ProjType).
 
 %% @doc Get all projections from the FLU's projection store.
 
--spec get_all_projections(inet_host(), inet_port(),
-               projection_type()) ->
-      {ok, [projection()]} | {error, term()}.
+-spec get_all_projections(machi_dt:inet_host(), machi_dt:inet_port(), machi_dt:projection_type()) ->
+      {ok, [machi_dt:projection()]} | {error, term()}.
 get_all_projections(Host, TcpPort, ProjType)
   when ProjType == 'public' orelse ProjType == 'private' ->
     Sock = connect(#p_srvr{proto_mod=?MODULE, address=Host, port=TcpPort}),
@@ -368,7 +342,7 @@ get_all_projections(Host, TcpPort, ProjType)
 
 %% @doc Get all epoch numbers from the FLU's projection store.
 
--spec list_all_projections(port_wrap(), projection_type()) ->
+-spec list_all_projections(port_wrap(), machi_dt:projection_type()) ->
       {ok, [non_neg_integer()]} | {error, term()}.
 list_all_projections(Sock, ProjType)
   when ProjType == 'public' orelse ProjType == 'private' ->
@@ -376,8 +350,7 @@ list_all_projections(Sock, ProjType)
 
 %% @doc Get all epoch numbers from the FLU's projection store.
 
--spec list_all_projections(inet_host(), inet_port(),
-                       projection_type()) ->
+-spec list_all_projections(machi_dt:inet_host(), machi_dt:inet_port(), machi_dt:projection_type()) ->
       {ok, [non_neg_integer()]} | {error, term()}.
 list_all_projections(Host, TcpPort, ProjType)
   when ProjType == 'public' orelse ProjType == 'private' ->
@@ -419,8 +392,8 @@ disconnect(_) ->
 %% @doc Restricted API: Write a chunk of already-sequenced data to
 %% `File' at `Offset'.
 
--spec write_chunk(port_wrap(), epoch_id(), file_name(), file_offset(), chunk()) ->
-      ok | {error, error_general()} | {error, term()}.
+-spec write_chunk(port_wrap(), machi_dt:epoch_id(), machi_dt:file_name(), machi_dt:file_offset(), machi_dt:chunk()) ->
+      ok | {error, machi_dt:error_general()} | {error, term()}.
 write_chunk(Sock, EpochID, File, Offset, Chunk)
   when Offset >= ?MINIMUM_OFFSET ->
     write_chunk2(Sock, EpochID, File, Offset, Chunk).
@@ -428,9 +401,9 @@ write_chunk(Sock, EpochID, File, Offset, Chunk)
 %% @doc Restricted API: Write a chunk of already-sequenced data to
 %% `File' at `Offset'.
 
--spec write_chunk(inet_host(), inet_port(),
-                  epoch_id(), file_name(), file_offset(), chunk()) ->
-      ok | {error, error_general()} | {error, term()}.
+-spec write_chunk(machi_dt:inet_host(), machi_dt:inet_port(),
+                  machi_dt:epoch_id(), machi_dt:file_name(), machi_dt:file_offset(), machi_dt:chunk()) ->
+      ok | {error, machi_dt:error_general()} | {error, term()}.
 write_chunk(Host, TcpPort, EpochID, File, Offset, Chunk)
   when Offset >= ?MINIMUM_OFFSET ->
     Sock = connect(#p_srvr{proto_mod=?MODULE, address=Host, port=TcpPort}),
@@ -443,16 +416,16 @@ write_chunk(Host, TcpPort, EpochID, File, Offset, Chunk)
 %% @doc Restricted API: Delete a file after it has been successfully
 %% migrated.
 
--spec delete_migration(port_wrap(), epoch_id(), file_name()) ->
-      ok | {error, error_general() | 'no_such_file'} | {error, term()}.
+-spec delete_migration(port_wrap(), machi_dt:epoch_id(), machi_dt:file_name()) ->
+      ok | {error, machi_dt:error_general() | 'no_such_file'} | {error, term()}.
 delete_migration(Sock, EpochID, File) ->
     delete_migration2(Sock, EpochID, File).
 
 %% @doc Restricted API: Delete a file after it has been successfully
 %% migrated.
 
--spec delete_migration(inet_host(), inet_port(), epoch_id(), file_name()) ->
-      ok | {error, error_general() | 'no_such_file'} | {error, term()}.
+-spec delete_migration(machi_dt:inet_host(), machi_dt:inet_port(), machi_dt:epoch_id(), machi_dt:file_name()) ->
+      ok | {error, machi_dt:error_general() | 'no_such_file'} | {error, term()}.
 delete_migration(Host, TcpPort, EpochID, File) when is_integer(TcpPort) ->
     Sock = connect(#p_srvr{proto_mod=?MODULE, address=Host, port=TcpPort}),
     try
@@ -464,16 +437,16 @@ delete_migration(Host, TcpPort, EpochID, File) when is_integer(TcpPort) ->
 %% @doc Restricted API: Truncate a file after it has been successfully
 %% erasure coded.
 
--spec trunc_hack(port_wrap(), epoch_id(), file_name()) ->
-      ok | {error, error_general() | 'no_such_file'} | {error, term()}.
+-spec trunc_hack(port_wrap(), machi_dt:epoch_id(), machi_dt:file_name()) ->
+      ok | {error, machi_dt:error_general() | 'no_such_file'} | {error, term()}.
 trunc_hack(Sock, EpochID, File) ->
     trunc_hack2(Sock, EpochID, File).
 
 %% @doc Restricted API: Truncate a file after it has been successfully
 %% erasure coded.
 
--spec trunc_hack(inet_host(), inet_port(), epoch_id(), file_name()) ->
-      ok | {error, error_general() | 'no_such_file'} | {error, term()}.
+-spec trunc_hack(machi_dt:inet_host(), machi_dt:inet_port(), machi_dt:epoch_id(), machi_dt:file_name()) ->
+      ok | {error, machi_dt:error_general() | 'no_such_file'} | {error, term()}.
 trunc_hack(Host, TcpPort, EpochID, File) when is_integer(TcpPort) ->
     Sock = connect(#p_srvr{proto_mod=?MODULE, address=Host, port=TcpPort}),
     try
diff --git a/src/machi_util.erl b/src/machi_util.erl
index aae5963..2b8fb97 100644
--- a/src/machi_util.erl
+++ b/src/machi_util.erl
@@ -48,7 +48,7 @@
 %% @doc Create a registered name atom for FLU sequencer internal
 %% rendezvous/message passing use.
 
--spec make_regname(binary()|list()) ->
+-spec make_regname(binary()|string()) ->
       atom().
 make_regname(Prefix) when is_binary(Prefix) ->
     erlang:binary_to_atom(Prefix, latin1);
@@ -231,13 +231,13 @@ make_tagged_csum(server_regen, SHA) ->
 
 %% @doc Log a verbose message.
 
--spec verb(string()) -> term().
+-spec verb(string()) -> ok.
 verb(Fmt) ->
     verb(Fmt, []).
 
 %% @doc Log a verbose message.
 
--spec verb(string(), list()) -> term().
+-spec verb(string(), list()) -> ok.
 verb(Fmt, Args) ->
     case application:get_env(kernel, verbose) of
         {ok, true} -> io:format(Fmt, Args);
diff --git a/src/machi_yessir_client.erl b/src/machi_yessir_client.erl
index c7e4872..d63aa2a 100644
--- a/src/machi_yessir_client.erl
+++ b/src/machi_yessir_client.erl
@@ -64,45 +64,15 @@
           chunk_size
          }).
 
--type chunk()       :: chunk_bin() | {chunk_csum(), chunk_bin()}.
--type chunk_bin()   :: binary() | iolist().    % client can use either
--type chunk_csum()  :: binary().               % 1 byte tag, N-1 bytes checksum
-%% -type chunk_summary() :: {file_offset(), chunk_size(), binary()}.
--type chunk_s()     :: binary().               % server always uses binary()
--type chunk_pos()   :: {file_offset(), chunk_size(), file_name_s()}.
--type chunk_size()  :: non_neg_integer().
--type error_general() :: 'bad_arg' | 'wedged'.
--type epoch_csum()  :: binary().
--type epoch_num()   :: -1 | non_neg_integer().
--type epoch_id()    :: {epoch_num(), epoch_csum()}.
--type file_info()   :: {file_size(), file_name_s()}.
--type file_name()   :: binary() | list().
--type file_name_s() :: binary().                % server reply
--type file_offset() :: non_neg_integer().
--type file_size()   :: non_neg_integer().
--type file_prefix() :: binary() | list().
--type inet_host()   :: inet:ip_address() | inet:hostname().
--type inet_port()   :: inet:port_number().
--type port_wrap()   :: #yessir{}. % yessir non-standard!
--type projection()      :: #projection_v1{}.
--type projection_type() :: 'public' | 'private'.
-
--export_type([epoch_id/0]).
-
 %% @doc Append a chunk (binary- or iolist-style) of data to a file
 %% with `Prefix'.
 
--spec append_chunk(port_wrap(), epoch_id(), file_prefix(), chunk()) ->
-      {ok, chunk_pos()} | {error, error_general()} | {error, term()}.
 append_chunk(Sock, EpochID, Prefix, Chunk) ->
     append_chunk_extra(Sock, EpochID, Prefix, Chunk, 0).
 
 %% @doc Append a chunk (binary- or iolist-style) of data to a file
 %% with `Prefix'.
 
--spec append_chunk(inet_host(), inet_port(),
-                   epoch_id(), file_prefix(), chunk()) ->
-      {ok, chunk_pos()} | {error, error_general()} | {error, term()}.
 append_chunk(_Host, _TcpPort, EpochID, Prefix, Chunk) ->
     Sock = connect(#p_srvr{proto_mod=?MODULE}),
     try
@@ -119,8 +89,6 @@ append_chunk(_Host, _TcpPort, EpochID, Prefix, Chunk) ->
 %% be reserved by the file sequencer for later write(s) by the
 %% `write_chunk()' API.
 
--spec append_chunk_extra(port_wrap(), epoch_id(), file_prefix(), chunk(), chunk_size()) ->
-      {ok, chunk_pos()}. %%%%  | {error, error_general()} | {error, term()}.
 append_chunk_extra(#yessir{name=Name,start_bin=StartBin},
                    _EpochID, Prefix, Chunk, ChunkExtra)
   when is_integer(ChunkExtra), ChunkExtra >= 0 ->
@@ -140,9 +108,6 @@ append_chunk_extra(#yessir{name=Name,start_bin=StartBin},
 %% be reserved by the file sequencer for later write(s) by the
 %% `write_chunk()' API.
 
--spec append_chunk_extra(inet_host(), inet_port(),
-                   epoch_id(), file_prefix(), chunk(), chunk_size()) ->
-      {ok, chunk_pos()}. %%%% | {error, error_general()} | {error, term()}.
 append_chunk_extra(_Host, _TcpPort, EpochID, Prefix, Chunk, ChunkExtra)
   when is_integer(ChunkExtra), ChunkExtra >= 0 ->
     Sock = connect(#p_srvr{proto_mod=?MODULE}),
@@ -154,10 +119,6 @@ append_chunk_extra(_Host, _TcpPort, EpochID, Prefix, Chunk, ChunkExtra)
 
 %% @doc Read a chunk of data of size `Size' from `File' at `Offset'.
 
--spec read_chunk(port_wrap(), epoch_id(), file_name(), file_offset(), chunk_size()) ->
-      {ok, chunk_s()} |
-      {error, error_general() | 'no_such_file' | 'partial_read'} |
-      {error, term()}.
 read_chunk(#yessir{name=Name}, _EpochID, File, Offset, Size)
   when Offset >= ?MINIMUM_OFFSET, Size >= 0 ->
     case get({Name,offset,File}) of
@@ -201,11 +162,6 @@ make_csum(Name,Size) ->
 
 %% @doc Read a chunk of data of size `Size' from `File' at `Offset'.
 
--spec read_chunk(inet_host(), inet_port(), epoch_id(),
-                 file_name(), file_offset(), chunk_size()) ->
-      {ok, chunk_s()} |
-      {error, error_general() | 'no_such_file' | 'partial_read'} |
-      {error, term()}.
 read_chunk(_Host, _TcpPort, EpochID, File, Offset, Size)
   when Offset >= ?MINIMUM_OFFSET, Size >= 0 ->
     Sock = connect(#p_srvr{proto_mod=?MODULE}),
@@ -217,10 +173,6 @@ read_chunk(_Host, _TcpPort, EpochID, File, Offset, Size)
 
 %% @doc Fetch the list of chunk checksums for `File'.
 
--spec checksum_list(port_wrap(), epoch_id(), file_name()) ->
-      {ok, [chunk_csum()]} |
-      {error, error_general() | 'no_such_file' | 'partial_read'} |
-      {error, term()}.
 checksum_list(#yessir{name=Name,chunk_size=ChunkSize}, _EpochID, File) ->
     case get({Name,offset,File}) of
         undefined ->
@@ -234,9 +186,6 @@ checksum_list(#yessir{name=Name,chunk_size=ChunkSize}, _EpochID, File) ->
 
 %% @doc Fetch the list of chunk checksums for `File'.
 
--spec checksum_list(inet_host(), inet_port(), epoch_id(), file_name()) ->
-      {ok, [chunk_csum()]} |
-      {error, error_general() | 'no_such_file'} | {error, term()}.
 checksum_list(_Host, _TcpPort, EpochID, File) ->
     Sock = connect(#p_srvr{proto_mod=?MODULE}),
     try
@@ -247,16 +196,12 @@ checksum_list(_Host, _TcpPort, EpochID, File) ->
 
 %% @doc Fetch the list of all files on the remote FLU.
 
--spec list_files(port_wrap(), epoch_id()) ->
-      {ok, [file_info()]} | {error, term()}.
 list_files(#yessir{name=Name}, _EpochID) ->
     Files = [{Offset, File} || {{N,offset,File}, Offset} <- get(), N == Name],
     {ok, Files}.
 
 %% @doc Fetch the list of all files on the remote FLU.
 
--spec list_files(inet_host(), inet_port(), epoch_id()) ->
-      {ok, [file_info()]} | {error, term()}.
 list_files(_Host, _TcpPort, EpochID) ->
     Sock = connect(#p_srvr{proto_mod=?MODULE}),
     try
@@ -267,16 +212,11 @@ list_files(_Host, _TcpPort, EpochID) ->
 
 %% @doc Fetch the wedge status from the remote FLU.
 
--spec wedge_status(port_wrap()) ->
-      {ok, {boolean(), pv1_epoch()}} | {error, term()}.
-
 wedge_status(_Sock) ->
     {ok, {false, ?DUMMY_PV1_EPOCH}}.
 
 %% @doc Fetch the wedge status from the remote FLU.
 
--spec wedge_status(inet_host(), inet_port()) ->
-      {ok, {boolean(), pv1_epoch()}} | {error, term()}.
 wedge_status(_Host, _TcpPort) ->
     Sock = connect(#p_srvr{proto_mod=?MODULE}),
     try
@@ -287,8 +227,6 @@ wedge_status(_Host, _TcpPort) ->
 
 %% @doc Get the latest epoch number + checksum from the FLU's projection store.
 
--spec get_latest_epoch(port_wrap(), projection_type()) ->
-      {ok, epoch_id()} | {error, term()}.
 get_latest_epoch(Sock, ProjType)
   when ProjType == 'public' orelse ProjType == 'private' ->
     case read_latest_projection(Sock, ProjType) of
@@ -298,9 +236,6 @@ get_latest_epoch(Sock, ProjType)
 
 %% @doc Get the latest epoch number + checksum from the FLU's projection store.
 
--spec get_latest_epoch(inet_host(), inet_port(),
-                       projection_type()) ->
-      {ok, epoch_id()} | {error, term()}.
 get_latest_epoch(_Host, _TcpPort, ProjType)
   when ProjType == 'public' orelse ProjType == 'private' ->
     Sock = connect(#p_srvr{proto_mod=?MODULE}),
@@ -312,8 +247,6 @@ get_latest_epoch(_Host, _TcpPort, ProjType)
 
 %% @doc Get the latest projection from the FLU's projection store for `ProjType'
 
--spec read_latest_projection(port_wrap(), projection_type()) ->
-      {ok, projection()} | {error, not_written} | {error, term()}.
 read_latest_projection(#yessir{name=Name}, ProjType)
   when ProjType == 'public' orelse ProjType == 'private' ->
     Ps = [P || {{N,proj,PT,_Epoch}, P} <- get(), N == Name, PT == ProjType],
@@ -330,9 +263,6 @@ read_latest_projection(#yessir{name=Name}, ProjType)
 
 %% @doc Get the latest projection from the FLU's projection store for `ProjType'
 
--spec read_latest_projection(inet_host(), inet_port(),
-                       projection_type()) ->
-      {ok, projection()} | {error, not_written} | {error, term()}.
 read_latest_projection(_Host, _TcpPort, ProjType)
   when ProjType == 'public' orelse ProjType == 'private' ->
     Sock = connect(#p_srvr{proto_mod=?MODULE}),
@@ -344,8 +274,6 @@ read_latest_projection(_Host, _TcpPort, ProjType)
 
 %% @doc Read a projection `Proj' of type `ProjType'.
 
--spec read_projection(port_wrap(), projection_type(), epoch_num()) ->
-      {ok, projection()} | {error, not_written} | {error, term()}.
 read_projection(#yessir{name=Name}, ProjType, Epoch)
   when ProjType == 'public' orelse ProjType == 'private' ->
     case get({Name,proj,ProjType,Epoch}) of
@@ -357,9 +285,6 @@ read_projection(#yessir{name=Name}, ProjType, Epoch)
 
 %% @doc Read a projection `Proj' of type `ProjType'.
 
--spec read_projection(inet_host(), inet_port(),
-                       projection_type(), epoch_num()) ->
-      {ok, projection()} | {error, written} | {error, term()}.
 read_projection(_Host, _TcpPort, ProjType, Epoch)
   when ProjType == 'public' orelse ProjType == 'private' ->
     Sock = connect(#p_srvr{proto_mod=?MODULE}),
@@ -371,8 +296,6 @@ read_projection(_Host, _TcpPort, ProjType, Epoch)
 
 %% @doc Write a projection `Proj' of type `ProjType'.
 
--spec write_projection(port_wrap(), projection_type(), projection()) ->
-      'ok' | {error, written} | {error, term()}.
 write_projection(#yessir{name=Name}=Sock, ProjType, Proj)
   when ProjType == 'public' orelse ProjType == 'private',
        is_record(Proj, projection_v1) ->
@@ -387,9 +310,6 @@ write_projection(#yessir{name=Name}=Sock, ProjType, Proj)
 
 %% @doc Write a projection `Proj' of type `ProjType'.
 
--spec write_projection(inet_host(), inet_port(),
-                       projection_type(), projection()) ->
-      'ok' | {error, written} | {error, term()}.
 write_projection(_Host, _TcpPort, ProjType, Proj)
   when ProjType == 'public' orelse ProjType == 'private',
        is_record(Proj, projection_v1) ->
@@ -402,8 +322,6 @@ write_projection(_Host, _TcpPort, ProjType, Proj)
 
 %% @doc Get all projections from the FLU's projection store.
 
--spec get_all_projections(port_wrap(), projection_type()) ->
-      {ok, [projection()]} | {error, term()}.
 get_all_projections(#yessir{name=Name}, ProjType)
   when ProjType == 'public' orelse ProjType == 'private' ->
     Ps = [Proj || {{N,proj,PT,_}, Proj} <- get(), N == Name, PT == ProjType],
@@ -411,9 +329,6 @@ get_all_projections(#yessir{name=Name}, ProjType)
 
 %% @doc Get all projections from the FLU's projection store.
 
--spec get_all_projections(inet_host(), inet_port(),
-               projection_type()) ->
-      {ok, [projection()]} | {error, term()}.
 get_all_projections(_Host, _TcpPort, ProjType)
   when ProjType == 'public' orelse ProjType == 'private' ->
     Sock = connect(#p_srvr{proto_mod=?MODULE}),
@@ -425,8 +340,6 @@ get_all_projections(_Host, _TcpPort, ProjType)
 
 %% @doc Get all epoch numbers from the FLU's projection store.
 
--spec list_all_projections(port_wrap(), projection_type()) ->
-      {ok, [non_neg_integer()]} | {error, term()}.
 list_all_projections(Sock, ProjType)
   when ProjType == 'public' orelse ProjType == 'private' ->
     case get_all_projections(Sock, ProjType) of
@@ -436,9 +349,6 @@ list_all_projections(Sock, ProjType)
 
 %% @doc Get all epoch numbers from the FLU's projection store.
 
--spec list_all_projections(inet_host(), inet_port(),
-                       projection_type()) ->
-      {ok, [non_neg_integer()]} | {error, term()}.
 list_all_projections(_Host, _TcpPort, ProjType)
   when ProjType == 'public' orelse ProjType == 'private' ->
     Sock = connect(#p_srvr{proto_mod=?MODULE}),
@@ -450,8 +360,6 @@ list_all_projections(_Host, _TcpPort, ProjType)
 
 %% @doc Quit &amp; close the connection to remote FLU.
 
--spec quit(port_wrap()) ->
-      ok.
 quit(_) ->
     ok.
 
@@ -460,8 +368,6 @@ quit(_) ->
 %% @doc Restricted API: Write a chunk of already-sequenced data to
 %% `File' at `Offset'.
 
--spec write_chunk(port_wrap(), epoch_id(), file_name(), file_offset(), chunk()) ->
-      ok | {error, error_general()} | {error, term()}.
 write_chunk(#yessir{name=Name}, _EpochID, File, Offset, Chunk)
   when Offset >= ?MINIMUM_OFFSET ->
     Pos = case get({Name,offset,File}) of
@@ -474,9 +380,6 @@ write_chunk(#yessir{name=Name}, _EpochID, File, Offset, Chunk)
 %% @doc Restricted API: Write a chunk of already-sequenced data to
 %% `File' at `Offset'.
 
--spec write_chunk(inet_host(), inet_port(),
-                  epoch_id(), file_name(), file_offset(), chunk()) ->
-      ok | {error, error_general()} | {error, term()}.
 write_chunk(_Host, _TcpPort, EpochID, File, Offset, Chunk)
   when Offset >= ?MINIMUM_OFFSET ->
     Sock = connect(#p_srvr{proto_mod=?MODULE}),
@@ -489,8 +392,6 @@ write_chunk(_Host, _TcpPort, EpochID, File, Offset, Chunk)
 %% @doc Restricted API: Delete a file after it has been successfully
 %% migrated.
 
--spec delete_migration(port_wrap(), epoch_id(), file_name()) ->
-      ok | {error, error_general() | 'no_such_file'} | {error, term()}.
 delete_migration(#yessir{name=Name}, _EpochID, File) ->
     case get({Name,offset,File}) of
         undefined ->
@@ -503,8 +404,6 @@ delete_migration(#yessir{name=Name}, _EpochID, File) ->
 %% @doc Restricted API: Delete a file after it has been successfully
 %% migrated.
 
--spec delete_migration(inet_host(), inet_port(), epoch_id(), file_name()) ->
-      ok | {error, error_general() | 'no_such_file'} | {error, term()}.
 delete_migration(_Host, _TcpPort, EpochID, File) ->
     Sock = connect(#p_srvr{proto_mod=?MODULE}),
     try
@@ -516,16 +415,12 @@ delete_migration(_Host, _TcpPort, EpochID, File) ->
 %% @doc Restricted API: Truncate a file after it has been successfully
 %% erasure coded.
 
--spec trunc_hack(port_wrap(), epoch_id(), file_name()) ->
-      ok | {error, error_general() | 'no_such_file'} | {error, term()}.
 trunc_hack(#yessir{name=Name}, _EpochID, File) ->
     put({Name,offset,File}, ?MINIMUM_OFFSET).
 
 %% @doc Restricted API: Truncate a file after it has been successfully
 %% erasure coded.
 
--spec trunc_hack(inet_host(), inet_port(), epoch_id(), file_name()) ->
-      ok | {error, error_general() | 'no_such_file'} | {error, term()}.
 trunc_hack(_Host, _TcpPort, EpochID, File) ->
     Sock = connect(#p_srvr{proto_mod=?MODULE}),
     try
diff --git a/test/machi_cr_client_test.erl b/test/machi_cr_client_test.erl
index 6466294..e6db150 100644
--- a/test/machi_cr_client_test.erl
+++ b/test/machi_cr_client_test.erl
@@ -135,6 +135,29 @@ smoke_test2() ->
         %% Exactly one file right now
         {ok, [_]} = machi_cr_client:list_files(C1),
 
+        %% Go back and test append_chunk_extra() and write_chunk()
+        Chunk10 = <<"It's a different chunk!">>,
+        Size10 = byte_size(Chunk10),
+        Extra10 = 5,
+        {ok, {Off10,Size10,File10}} =
+            machi_cr_client:append_chunk_extra(C1, Prefix, Chunk10,
+                                               Extra10 * Size10),
+        {ok, Chunk10} = machi_cr_client:read_chunk(C1, File10, Off10, Size10),
+        [begin
+             Offx = Off10 + (Seq * Size10),
+             %% TODO: uncomment written/not_written enforcement is available.
+             %% {error,not_written} = machi_cr_client:read_chunk(C1, File10,
+             %%                                                  Offx, Size10),
+             {ok, {Offx,Size10,File10}} =
+                 machi_cr_client:write_chunk(C1, File10, Offx, Chunk10),
+             {ok, Chunk10} = machi_cr_client:read_chunk(C1, File10, Offx,
+                                                        Size10)
+         end || Seq <- lists:seq(1, Extra10)],
+        {ok, {Off11,Size11,File11}} =
+            machi_cr_client:append_chunk(C1, Prefix, Chunk10),
+        %% Double-check that our reserved extra bytes were really honored!
+        true = (Off11 > (Off10 + (Extra10 * Size10))),
+
         ok
     after
         error_logger:tty(true),
diff --git a/test/machi_pb_cr_client_test.erl b/test/machi_pb_cr_client_test.erl
new file mode 100644
index 0000000..483ab9d
--- /dev/null
+++ b/test/machi_pb_cr_client_test.erl
@@ -0,0 +1,79 @@
+%% -------------------------------------------------------------------
+%%
+%% Copyright (c) 2007-2015 Basho Technologies, Inc.  All Rights Reserved.
+%%
+%% This file is provided to you under the Apache License,
+%% Version 2.0 (the "License"); you may not use this file
+%% except in compliance with the License.  You may obtain
+%% a copy of the License at
+%%
+%%   http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing,
+%% software distributed under the License is distributed on an
+%% "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+%% KIND, either express or implied.  See the License for the
+%% specific language governing permissions and limitations
+%% under the License.
+%%
+%% -------------------------------------------------------------------
+
+-module(machi_pb_cr_client_test).
+-compile(export_all).
+
+-ifdef(TEST).
+-ifndef(PULSE).
+
+-include("machi_pb.hrl").
+-include("machi_projection.hrl").
+-include_lib("eunit/include/eunit.hrl").
+
+-define(C, machi_pb_cr_client).
+
+smoke_test_() ->
+    {timeout, 5*60, fun() -> smoke_test2() end}.
+
+smoke_test2() ->
+    Port = 5720,
+    Ps = [{a,#p_srvr{name=a, address="localhost", port=Port, props="./data.a"}}
+         ],
+    
+    [os:cmd("rm -rf " ++ P#p_srvr.props) || {_,P} <- Ps],
+    {ok, SupPid} = machi_flu_sup:start_link(),
+    try
+        [begin
+             #p_srvr{name=Name, port=Port, props=Dir} = P,
+             {ok, _} = machi_flu_psup:start_flu_package(Name, Port, Dir, [])
+         end || {_,P} <- Ps],
+        [machi_chain_manager1:test_react_to_env(a_chmgr) || _ <-lists:seq(1,5)],
+
+        {_, P_a} = hd(Ps),
+        {ok, Sock} = gen_tcp:connect(P_a#p_srvr.address, P_a#p_srvr.port,
+                                     [{packet, line}, binary, {active, false}]),
+        try
+            Prefix = <<"pre">>,
+            Chunk1 = <<"yochunk">>,
+            ok = gen_tcp:send(Sock, <<"PROTOCOL-BUFFERS\n">>),
+            {ok, <<"OK\n">>} = gen_tcp:recv(Sock, 0),
+            ok = inet:setopts(Sock, [{packet,4}]),
+            R1a = #mpb_request{req_id= <<0>>,
+                               echo=#mpb_echoreq{message = <<"Hello, world!">>}},
+            Bin1a = machi_pb:encode_mpb_request(R1a),
+            ok = gen_tcp:send(Sock, Bin1a),
+            {ok, Bin1B} = gen_tcp:recv(Sock, 0),
+            R1b = machi_pb:decode_mpb_response(Bin1B),
+            true = is_record(R1b, mpb_response),
+
+            ok
+        after
+            (catch gen_tcp:close(Sock))
+        end
+    after
+        exit(SupPid, normal),
+        [os:cmd("rm -rf " ++ P#p_srvr.props) || {_,P} <- Ps],
+        machi_util:wait_for_death(SupPid, 100),
+        ok
+    end.
+
+-endif. % !PULSE
+-endif. % TEST
diff --git a/test/machi_pb_test.erl b/test/machi_pb_test.erl
new file mode 100644
index 0000000..41a224f
--- /dev/null
+++ b/test/machi_pb_test.erl
@@ -0,0 +1,67 @@
+%% -------------------------------------------------------------------
+%%
+%% Machi: a small village of replicated files
+%%
+%% Copyright (c) 2014-2015 Basho Technologies, Inc.  All Rights Reserved.
+%%
+%% This file is provided to you under the Apache License,
+%% Version 2.0 (the "License"); you may not use this file
+%% except in compliance with the License.  You may obtain
+%% a copy of the License at
+%%
+%%   http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing,
+%% software distributed under the License is distributed on an
+%% "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+%% KIND, either express or implied.  See the License for the
+%% specific language governing permissions and limitations
+%% under the License.
+%%
+%% -------------------------------------------------------------------
+-module(machi_pb_test).
+
+-include("machi_pb.hrl").
+
+-compile(export_all).
+
+-ifdef(TEST).
+-ifndef(PULSE).
+
+-include_lib("eunit/include/eunit.hrl").
+
+%% We don't expect any problems with these functions: nearly all
+%% code executed is compiled from the PB definition file(s) and so
+%% ought to be bug-free.  Errors are likely to be caused by
+%% changes in the spec but without corresponding changes to
+%% message types/names here.
+
+smoke_requests_test() ->
+    Echo0 = #mpb_request{req_id= <<"x">>,
+                         echo=#mpb_echoreq{}},
+    Echo0 = encdec_request(Echo0),
+    Echo1 = #mpb_request{req_id= <<"x">>,
+                         echo=#mpb_echoreq{message="Yo!"}},
+    Echo1 = encdec_request(Echo1),
+
+    ok.
+
+smoke_responses_test() ->
+    R1 = #mpb_response{req_id= <<"x">>,
+                       generic=#mpb_errorresp{code=7,
+                                              msg="foo",
+                                              extra= <<"bar">>}},
+    R1 = encdec_response(R1),
+
+    ok.
+
+encdec_request(M) ->
+    machi_pb:decode_mpb_request(
+      list_to_binary(machi_pb:encode_mpb_request(M))).
+
+encdec_response(M) ->
+    machi_pb:decode_mpb_response(
+      list_to_binary(machi_pb:encode_mpb_response(M))).
+
+-endif. % !PULSE
+-endif. % TEST