Hello Eric On Tue, Feb 11, 2020 at 1:49 AM Erich Eckner wrote:

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On Tue, 11 Feb 2020, Anatol Pomozov wrote:

...

Hello folks

Hi Anatol,

...

While working on multiplexed download API I hit one issue that requires some alpm API changes.

Current ALPM download api handles one file at a time. And interaction between pacman and ALPM looks like:

- pacman iterates over list of files to download - pacman calls alpm API to download one file - alpm initializes curl with progress callback implemented by pacman - during the download curl calls the pacman callback - once download is done alpm returns a result code of the download transaction

In this single-download scenario pacman knows when the download starts, progresses and finished.

With multiplexed download feature alpm_download() will change its API. It will get a list of files as a parameter and handle downloads for all of them with a single function call.

This unfortunately makes impossible to intercept "start file download"

and

...

"complete file download" events. These events are needed because we want to render UI correctly and print download information like "file up to date", "failed to download"... at the exact moment when the event happens.

To mitigate this problem I propose to extend the callback API to make it possible for ALPM to provide other types of download events.

The signature will change from: typedef void (*alpm_cb_download)(const char *filename, off_t xfered, off_t total); that implies only download progress events, to: typedef void (*alpm_cb_download)(const char *filename, alpm_download_event_type_t event, void *data);

where alpm_download_event_type_t is enum

typedef enum { ALPM_DOWNLOAD_INIT, ALPM_DOWNLOAD_PROGRESS, ALPM_DOWNLOAD_ERROR, ALPM_DOWNLOAD_COMPLETED } alpm_download_event_type_t;

and *data is a pointer to event specific structure (different for each type of event), e.g.: typedef struct { int result; /* 1 - file is uptodate, 0 - download completed successfully, -1 failed */ } alpm_download_event_completed_t;

Note this is an ALPM breaking API change. It means it can be done only with major version bump.

What do you think about it?

I'm sure, you have considered this, but: Why not only(?) add a "this_event_refers_to_that_file" pointer of some kind to the callback (the index of the file in the parameter array, for example)? This might be nice, even if you change the interface in the direction you proposed. Then the frontend could update the progress/status of the respective file separately (xfered==0 would be "start", xfered==total would be "finished").

I am not fully understand your question. To answer it better could you please give a signature of the function you propose? Or is this, what "const char *filename" gets used for in the callback? filename is a name of the file we download. It is unique for a given multiplexed_download transaction so it can be used as a key to lookup the state of this particular download.

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 On Tue, 11 Feb 2020, Anatol Pomozov wrote:

Hello Eric

On Tue, Feb 11, 2020 at 1:49 AM Erich Eckner wrote:

...

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256

On Tue, 11 Feb 2020, Anatol Pomozov wrote:

...

Hello folks

Hi Anatol,

...

While working on multiplexed download API I hit one issue that requires some alpm API changes.

Current ALPM download api handles one file at a time. And interaction between pacman and ALPM looks like:

- pacman iterates over list of files to download - pacman calls alpm API to download one file - alpm initializes curl with progress callback implemented by pacman - during the download curl calls the pacman callback - once download is done alpm returns a result code of the download transaction

In this single-download scenario pacman knows when the download starts, progresses and finished.

With multiplexed download feature alpm_download() will change its API. It will get a list of files as a parameter and handle downloads for all of them with a single function call.

This unfortunately makes impossible to intercept "start file download"

and

...

"complete file download" events. These events are needed because we want to render UI correctly and print download information like "file up to date", "failed to download"... at the exact moment when the event happens.

To mitigate this problem I propose to extend the callback API to make it possible for ALPM to provide other types of download events.

The signature will change from: typedef void (*alpm_cb_download)(const char *filename, off_t xfered, off_t total); that implies only download progress events, to: typedef void (*alpm_cb_download)(const char *filename, alpm_download_event_type_t event, void *data);

where alpm_download_event_type_t is enum

typedef enum { ALPM_DOWNLOAD_INIT, ALPM_DOWNLOAD_PROGRESS, ALPM_DOWNLOAD_ERROR, ALPM_DOWNLOAD_COMPLETED } alpm_download_event_type_t;

and *data is a pointer to event specific structure (different for each type of event), e.g.: typedef struct { int result; /* 1 - file is uptodate, 0 - download completed successfully, -1 failed */ } alpm_download_event_completed_t;

Note this is an ALPM breaking API change. It means it can be done only with major version bump.

What do you think about it?

I'm sure, you have considered this, but: Why not only(?) add a "this_event_refers_to_that_file" pointer of some kind to the callback (the index of the file in the parameter array, for example)? This might be nice, even if you change the interface in the direction you proposed. Then the frontend could update the progress/status of the respective file separately (xfered==0 would be "start", xfered==total would be "finished").

I am not fully understand your question. To answer it better could you please give a signature of the function you propose?

My idea was to extend the current interface by just additionally referencing the file to which the callback-call refers to: typedef void (*alpm_cb_download)(const char *filename, int file_idx, off_t xfered, off_t total); so the callback function would know, for which file the reported progress is. But your interface seems superior to this, because it's more flexible.

Or is this, what "const char *filename" gets used for in the callback?

filename is a name of the file we download. It is unique for a given multiplexed_download transaction so it can be used as a key to lookup the state of this particular download.

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