836455 - nptest.cpp:1392:48: error: ignoring return value of ‘size_t fread(void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Werror=unused-result]

Status: RESOLVED FIXED

(Core :: Plug-ins, defect, P3)

Description

[Daniel Holbert [:dholbert]]

When I try to do a local opt build w/ --enable-warnings-as-errors, I get this build error:
{
dom/plugins/test/testplugin/nptest.cpp: In function ‘void NPP_StreamAsFile(NPP, NPStream*, const char*)’:
plugins/test/testplugin/nptest.cpp:1392:48: error: ignoring return value of ‘size_t fread(void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Werror=unused-result]
}

Looks like we need to just sanity-check the return value of fread().

Comment 1

[Benjamin Smedberg]

Or unused << since this is test code.

Comment 2

[Daniel Holbert [:dholbert]]

We apparently tried that before, and it triggers linking errors. See bug 754198 comment 9.

Might as well just fix this the "right" way (checking the return value), and not worry about those linking errors.

Comment 3

[Daniel Holbert [:dholbert]]

Attachment: fix

Comment 4

[Daniel Holbert [:dholbert]]

Comment on attachment 708281 [details] [diff] [review]
fix

>-    fread(instanceData->fileBuf, 1, size, file);
>+    size_t sizeRead = fread(instanceData->fileBuf, 1, size, file);
>+    if (sizeRead != size) {

Just to decode this, if you don't know fread()'s parameters by heart:

We're attempting to read 'size' chunks of data, w/ each chunk having a length of '1', from file, into fileBuf.  So, read 'size' bytes.

The return value is the number of chunks read -- so, i.e. the number of bytes read, since our chunk size is 1. So if all is well, it should return 'size'.

Comment 5

[Daniel Holbert [:dholbert]]

Green linux/mac try run:  https://tbpl.mozilla.org/?tree=Try&rev=517774a31e08

Landed: https://hg.mozilla.org/mozilla-central/rev/96c341954032