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Support reading script source from stdin in qjs #947

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Merged
merged 1 commit into from
Mar 3, 2025
Merged

Support reading script source from stdin in qjs #947

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4 changes: 3 additions & 1 deletion qjs.c
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Original file line number Diff line number Diff line change
Expand Up @@ -120,7 +120,9 @@ static int eval_buf(JSContext *ctx, const void *buf, int buf_len,
val = JS_Eval(ctx, buf, buf_len, filename,
eval_flags | JS_EVAL_FLAG_COMPILE_ONLY);
if (!JS_IsException(val)) {
use_realpath = (*filename != '<'); // ex. "<cmdline>"
// ex. "<cmdline>" pr "/dev/stdin"
use_realpath =
!(*filename == '<' || !strncmp(filename, "/dev/", 5));
if (js_module_set_import_meta(ctx, val, use_realpath, true) < 0) {
js_std_dump_error(ctx);
ret = -1;
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60 changes: 26 additions & 34 deletions quickjs-libc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -418,45 +418,37 @@ static JSValue js_printf_internal(JSContext *ctx,
uint8_t *js_load_file(JSContext *ctx, size_t *pbuf_len, const char *filename)
{
FILE *f;
uint8_t *buf;
size_t buf_len;
long lret;
size_t n, len;
uint8_t *p, *buf, tmp[8192];

f = fopen(filename, "rb");
if (!f)
return NULL;
if (fseek(f, 0, SEEK_END) < 0)
goto fail;
lret = ftell(f);
if (lret < 0)
goto fail;
/* XXX: on Linux, ftell() return LONG_MAX for directories */
if (lret == LONG_MAX) {
errno = EISDIR;
goto fail;
}
buf_len = lret;
if (fseek(f, 0, SEEK_SET) < 0)
goto fail;
if (ctx)
buf = js_malloc(ctx, buf_len + 1);
else
buf = malloc(buf_len + 1);
if (!buf)
goto fail;
if (fread(buf, 1, buf_len, f) != buf_len) {
errno = EIO;
if (ctx)
js_free(ctx, buf);
else
free(buf);
fail:
fclose(f);
return NULL;
}
buf[buf_len] = '\0';
buf = NULL;
len = 0;
do {
n = fread(tmp, 1, sizeof(tmp), f);
Comment on lines +429 to +430
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Why not use a regular loop while ((n = fread(tmp, 1, sizeof(tmp), f)) != 0) { ... }?
I the goal is to make sure buf is allocated for empty files, an explanatory comment would be welcome.

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Isn't that self-evident though? do/while is for when a loop should execute at least once.

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@chqrlie chqrlie Mar 4, 2025 •
edited
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do/while loops are never self evident, IME they have a tendency to hide nasty bugs. Whenever you see one in code, read carefully and you might find a bug.
In this case, the loop runs at least once, and fread will return 0 on empty files, so the case of a 0 return must be handled gracefully. And as an extra bonus, the loop will run one extra time on file whose length is exactly a multiple of 8K. That's 2 corner cases to think about. With a regular while loop, there is no hidden special cases to take into consideration. Less brain space: unambiguous end test and explicit empty file test.

if (ctx) {
p = js_realloc(ctx, buf, len + n + 1);
} else {
p = realloc(buf, len + n + 1);
}
if (!p) {
if (ctx) {
js_free(ctx, buf);
} else {
free(buf);
}
fclose(f);
return NULL;
}
memcpy(&p[len], tmp, n);
buf = p;
len += n;
buf[len] = '\0';
} while (n == sizeof(tmp));
fclose(f);
*pbuf_len = buf_len;
*pbuf_len = len;
return buf;
}

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