Here is a list of all documented files with brief descriptions:

src
base64.c
buf.c
buf.h	Buffers that map between stdio file streams and librsync streams
checksum.c
checksum.h	Abstract wrappers around different weaksum and strongsum implementations
command.c
command.h	Types of commands present in the encoding stream
delta.c	Generate in streaming mode an rsync delta given a set of signatures, and a new file
emit.c
emit.h	Encoding output routines
fileutil.c
hashtable.c
hashtable.h	A generic open addressing hashtable
hex.c
isprefix.c
isprefix.h	String prefix text function
job.c
job.h	Generic state-machine interface
librsync.h	Public header for librsync
librsync_export.h
mdfour.c
mdfour.h	MD4 message digest algorithm
mksum.c	Generate file signatures
msg.c	Error messages for re_result values
netint.c
netint.h	Network-byte-order output to the tube
patch.c	Apply a delta to an old file to generate a new file
prototab.c
prototab.h	Delta file commands
rabinkarp.c
rabinkarp.h	The rabinkarp class implementation of the RabinKarp rollsum
rdiff.c	Command-line network-delta tool
readsums.c	Load signatures from a file
rollsum.c
rollsum.h	The Rollsum class implementation of the original rsync rollsum
scoop.c	This file deals with readahead from caller-supplied buffers
scoop.h	Manage librsync streams of IO
stats.c	Stats reporting functions
sumset.c
sumset.h	The rs_signature class implementation of a file signature
trace.c
trace.h	Logging functions
tube.c	A somewhat elastic but fairly small buffer for data passing through a stream
util.c
util.h	Misc utility functions used by librsync
version.c
whole.c
whole.h	Whole-file API driver functions