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gp_camera_file_read vs. gp_camera_file_get #101

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peterbud opened this issue Oct 15, 2016 · 5 comments
Open

gp_camera_file_read vs. gp_camera_file_get #101

peterbud opened this issue Oct 15, 2016 · 5 comments
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@msmeissn

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@peterbud
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peterbud commented Oct 15, 2016 •
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I was using the sample program sample-capture and sample-trigger-capture, and found the following on my Windows port:

  • call to function gp_camera_file_get used in sample-capture WORKS, captures 2 images (both way) without any problem
  • call to function gp_camera_file_read used in sample-trigger-capture with the same camera and setting FAILS. As far as I can debug, gp_camera_file_read calls gp_filesystem_read_file, which then calls read_file_func. This one impleneted in ptp2/libary.c, and has a define for folder_to_storage, which expects that the folder paramter should have the name like "/store_xxxxxxxxx/"

Question: is this really a necessary check? Why then the gp_camera_file_get works perfectly?

Sorry if the question is stupid, I have started getting familiar with the library only recently.
@romainreignier
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I have faced the same issue.
I wanted to avoid the unnecessary write/delete operation on host filesystem.
But I have figured out that the function gp_camera_file_read is never used in the libgphoto2 and gphoto2.

@romainreignier
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In my case, for a Sony PTP camera, the path->folder value is overridden in the capture function here:

libgphoto2/camlibs/ptp2/library.c

Line 4215 in bc181c8

sprintf (path->folder,"/");

So the check in folder_to_storage cannot be valid.

@romainreignier
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Removing the folder_to_storage check does not help, the function fail later because the file is not found.
Because the gp_camera_file_read is never called I doubt it will work out of the box for ptp camera.
@msmeissn what do you think about it?

@msmeissn msmeissn self-assigned this Dec 27, 2018
@msmeissn
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Hmm. The gp_camera_file_read does not cover this case, it should check the filesystem backed cached storage here. This is missing. the _read function is not complete :/

But gp_camera_file_get() does not touch the host filesystem, unless you use gp_file_new_from_fd() or so, so you can still use that.

@romainreignier
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Oh! I've missed the point that I can initialize a CameraFile from memory with gp_file_new() and not gp_file_new_from_fd().
Thanks.
Until now, I was creating a temporary file with mkstemp() and then delete it with unlink().

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@msmeissn @peterbud @romainreignier