FreeRADIUS / sbuff

A separate repository for the sbuff string manipulation library

sbuff

A separate repository for the FreeRADIUS sbuff string manipulation library.

Introduction

Sbuffs are used internally within FreeRADIUS for safe string printing and parsing.

When used correctly sbuffs avoid many of the pitfalls of C string handling including buffer overflows and reads into uninitialised memory.

sbuff variants

There are four sbuff variants.

• I/O sbuffs which read from and write to network sockets or files. These sbuffs create a 'window' into the stream when reading, and (optionally) buffer data when writing.
• transform sbuffs, which apply transformations to data. This transformation is usually escaping or unescaping data. Transform sbuffs create a new window and stream, and all positions downstream of this sbuff are relative to the new stream.
• terminal sbuffs prevent reading past a sequence of characters in the stream.
• marker sbuffs which prevent the window of a transform or I/O sbuff going out of range. i.e. pinning a certain range of data within a parent's window.

memory usage

Sbuffs which create new windows, necessarily need

Reading/Parsing

Sbuffs can have an infinite number of children.

When parsing, each sbuff can control how much of a string are available to decendent sbuffs and perform transformations using intermediary buffers. The shallowest (top level) sbuff can also read/write data to/from streaming sources such as sockets and files.

These operations are driven by demands for data. When one of the sbuff_read_* functions is called, it will attempt to read however many bytes it needs to complete the operation from the sbuff that was passed into it, which may in turn attempt to read data from the previous sbuff in the chain.

Error indication

sbuff printing and parsing functions always return a sbuff_slen_t (typedef of ssize_t).

Reading

• >=0 the number of bytes consumed from the sbuff_t.
• <0 negative offset of where a parse error occurred. Given the string foo, and a return value of -1, a parse error would be indicated at offset 0 (f).

Writing

• >=0 the number of bytes written to the sbuff_t.
• <0 negative offset indicating how many additional bytes would be required in the sbuff to write the complete string. A return value of -5 would mean 5 more bytes would be required.