Z_BEST_SPEED doesn't handle Z_FINISH properly in some corner cases when there is not enough avail_out

[glandium]

Consider the following code:

#include <zlib.h>
#include <assert.h>
#include <string.h>
#include <stdio.h>

int main() {
    Bytef buf[4096];
    for (int i = 0; i < sizeof(buf); i++) {
        buf[i] = (i / 4) & 0xff;
    }
    Bytef out[4096];
    z_stream zs;
    memset(&zs, 0, sizeof(zs));
    int ret = deflateInit(&zs, Z_BEST_SPEED);
    assert(ret == Z_OK);
    zs.avail_in = 2048;
    zs.avail_out = 2048;
    zs.next_in = buf;
    zs.next_out = out;
    ret = deflate(&zs, Z_NO_FLUSH);
    assert(ret == Z_OK);

    zs.avail_in = 2048;
    zs.avail_out = 9;
    ret = deflate(&zs, Z_FINISH);
    assert(zs.avail_in == 0);
    return 0;
}

This works properly with zlib, but fails on the last assert with libz-rs-sys because zs.avail_in is still 2048.

Now, in this specific case, it still works afterwards (removing the last assert):

    zs.avail_out = sizeof(out) - zs.total_out;
    ret = deflate(&zs, Z_FINISH);
    assert(ret == Z_STREAM_END);
    assert(zs.avail_in == 0);

But depending on the input, you can end up with ret at Z_BUF_ERROR because it doesn't want avail_in to be non-zero, hitting the following code: https://github.com/memorysafety/zlib-rs/blob/e83fcefadb576e0ce32297cc516facb694d93b67/zlib-rs/src/deflate.rs#L2412-L2417

I haven't looked exactly why this isn't happening in the case above, but here's a testcase where it does happen:

testcase

include <zlib.h>
#include <assert.h>
#include <string.h>
#include <stdio.h>
#include <sys/mman.h>
#include <fcntl.h>

int main() {
    int fd = open("file.js", O_RDONLY);
    off_t len = lseek(fd, 0, SEEK_END);
    Bytef *buf = mmap(NULL, len, PROT_READ, MAP_PRIVATE, fd, 0);
    Bytef out[4096];
    z_stream zs;
    memset(&zs, 0, sizeof(zs));
    int ret = deflateInit2(&zs, Z_BEST_SPEED, Z_DEFLATED, -15, 8, Z_DEFAULT_STRATEGY);
    assert(ret == Z_OK);
    zs.avail_in = 2048;
    zs.avail_out = 1053;
    zs.next_in = buf;
    zs.next_out = out;
    ret = deflate(&zs, Z_NO_FLUSH);
    assert(ret == Z_OK);

    zs.avail_in = 67;
    ret = deflate(&zs, Z_FINISH);

    zs.avail_out = sizeof(out) - zs.total_out;
    ret = deflate(&zs, Z_FINISH);
    assert(ret == Z_STREAM_END);
    assert(zs.avail_in == 0);
    return 0;
}

file.js:

// This file was procedurally generated from the following sources:
// - src/dstr-binding/ary-init-iter-get-err.case
// - src/dstr-binding/error/cls-expr-async-gen-meth-static.template
/*---
description: Abrupt completion returned by GetIterator (static class expression async generator method)
esid: sec-class-definitions-runtime-semantics-evaluation
features: [Symbol.iterator, async-iteration]
flags: [generated]
info: |
    ClassExpression : class BindingIdentifieropt ClassTail

    1. If BindingIdentifieropt is not present, let className be undefined.
    2. Else, let className be StringValue of BindingIdentifier.
    3. Let value be the result of ClassDefinitionEvaluation of ClassTail
       with argument className.
    [...]

    14.5.14 Runtime Semantics: ClassDefinitionEvaluation

    21. For each ClassElement m in order from methods
        a. If IsStatic of m is false, then
        b. Else,
           Let status be the result of performing PropertyDefinitionEvaluation
           for m with arguments F and false.
    [...]

    Runtime Semantics: PropertyDefinitionEvaluation

    AsyncGeneratorMethod :
        async [no LineTerminator here] * PropertyName ( UniqueFormalParameters )
            { AsyncGeneratorBody }

    1. Let propKey be the result of evaluating PropertyName.
    2. ReturnIfAbrupt(propKey).
    3. If the function code for this AsyncGeneratorMethod is strict mode code, let strict be true.
       Otherwise let strict be false.
    4. Let scope be the running execution context's LexicalEnvironment.
    5. Let closure be ! AsyncGeneratorFunctionCreate(Method, UniqueFormalParameters,
       AsyncGeneratorBody, scope, strict).
    [...]

    13.3.3.5 Runtime Semantics: BindingInitialization

    BindingPattern : ArrayBindingPattern

    1. Let iterator be GetIterator(value).
    2. ReturnIfAbrupt(iterator).

---*/
var iter = {};
iter[Symbol.iterator] = function() {
  throw new Test262Error();
};


var C = class {
  static async *method([x]) {
    
  }
};

var method = C.method;

assert.throws(Test262Error, function() {
  method(iter);
});

reportCompare(0, 0);

Note: any other value of avail_out makes it not happen. Note that this value was picked because it's half the size of file.js.