tor

@dir /lib/container @brief lib/container: Hash tables, dynamic arrays, bit arrays, etc.

Smartlists: Neither lists, nor especially smart.

For historical reasons, we call our dynamic-allocated array type smartlist_t. It can grow or shrink as elements are added and removed.

All smartlists hold an array of void *. Whenever you expose a smartlist in an API you must document which types its pointers actually hold.

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Smartlists are created empty with smartlist_new() and freed with smartlist_free(). See the containers.h header documentation for more information; there are many convenience functions for commonly needed operations.

For low-level operations on smartlists, see also \refdir{lib/smartlist_core}.

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Digest maps, string maps, and more.

Tor makes frequent use of maps from 160-bit digests, 256-bit digests, or nul-terminated strings to void *. These types are digestmap_t, digest256map_t, and strmap_t respectively. See the containers.h module documentation for more information.

Intrusive lists and hashtables

For performance-sensitive cases, we sometimes want to use "intrusive" collections: ones where the bookkeeping pointers are stuck inside the structures that belong to the collection. If you've used the BSD-style sys/queue.h macros, you'll be familiar with these.

Unfortunately, the sys/queue.h macros vary significantly between the platforms that have them, so we provide our own variants in ext/tor_queue.h.

We also provide an intrusive hashtable implementation in ext/ht.h. When you're using it, you'll need to define your own hash functions. If attacker-induced collisions are a worry here, use the cryptographic siphash24g function to extract hashes.

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