Uploading symbols


Tecken lets you upload symbols. It stores these symbols files allowing others to use the download API to access them for symbolicating stacks, profiling, debugging, etc.

When building software, you can run dump_syms to extract debugging information and generate Breakpad symbol files.

You can upload your symbols ZIP file to Tecken using the upload API.

Symbols ZIP file structure

ZIP files must consist of Breakpad symbol files in this structure:


For example, here’s the contents of a symbols ZIP file from a Firefox build:


Permissions and auth token

Uploading requires two things:

  1. an account with upload permissions

  2. an auth token for that account with upload permissions

The auth token is used in the HTTP POST to authenticate the upload.

Try symbols

Tecken differentiates “release builds” from “try builds”.

Try builds can be kicked off by anyone and are typically used to debug or test changes. There are many more Try builds than there are release builds. Try builds tend to be more ephemeral and not very interesting after a week or two.

For this reason, Tecken lets you differentiate between “release builds” and “try builds”. Try build symbols won’t override release build symbols. Try build symbols files expire from our system after 28 days.

There are two ways to upload symbols for try builds:

  1. Use an auth token with “Upload Try Symbols” permission.

  2. Include try=1 in the HTTP POST data.

Example with curl:

$ curl --user-agent "example/1.0" -X POST -H 'auth-token: xxx' \
    --form try=1 \
    --form myfile.zip=@myfile.zip \

See the Try builds documentation under Download.

Two ways to upload symbols

While there is one API endpoint, there are two different ways to upload symbols.

  1. Including the symbols ZIP file in the HTTP POST.

  2. Uploading the ZIP file to a publicly available URL and then specifying that URL in the HTTP POST.

Upload by HTTP POST (payload < 2gb size)

Include the ZIP file in the HTTP POST to /upload/ as a multipart/form-data payload.

Here’s a curl example:

$ curl --user-agent "example/1.0" -X POST -H 'auth-token: xxx' \
    --form myfile.zip=@myfile.zip \

Here’s a Python example using the requests library:

>>> import requests
>>> files = {"myfile.zip": open("path/to/myfile.zip", "rb")}
>>> url = "https://symbols.mozilla.org/upload/"
>>> headers = {"User-Agent": "example/1.0", "Auth-token": "xxx"}
>>> response = requests.post(url, files=files, headers=headers)
>>> response.status_code

This works if the HTTP POST is less than 2gb. If the HTTP POST request is larger than 2gb, then you’ll need to use upload by download url.

Upload by download url (payload > 2gb size)

Upload the symbols file to some publicly available URL at an approved domain.

Then do an HTTP POST to /upload/ as a application/x-www-form-urlencoded payload and specify the url to the symbols file as a value to url.

Domains that Tecken will download from is specified in the DJANGO_ALLOW_UPLOAD_BY_DOWNLOAD_DOMAINS environment variable and at the time of this writing is set to:


If you need another domain supported, file a bug.

Tecken will check redirects. At first a HEAD request is made with the URL and Tecken will check both the original URL and the redirected URL against the list of allowed URLs.

An example with curl:

$ curl --user-agent "example/1.0" -X POST -H 'auth-token: xxx' \
   -d url="https://queue.taskcluster.net/YC0FgOlE/artifacts/symbols.zip" \

An example with Python and the requests library:

>>> import requests
>>> url = "https://symbols.mozilla.org/upload/"
>>> headers = {"User-Agent": "example/1.0", "Auth-token": "xxx"}
>>> data = {"url": "https://queue.taskcluster.net/YC0FgOlE/artifacts/symbols.zip"}
>>> response = requests.post(url, data=data, headers=headers)
>>> response.status_code

Permissions and auth tokens

Uploading symbols to Tecken requires special permission. The process for requesting access to upload symbols is roughly the following:

  1. Create a bug requesting access to upload symbols.

  2. A Tecken admin will process the request.

    If you are a Mozilla employee, your manager will be needinfo’d to verify you need upload access.

    If you are not a Mozilla employee, we’ll need to find someone to vouch for you.

  3. After that’s been worked out, the Tecken admin will give you permission to upload symbols.

Once you have permission to upload symbols, you will additionally need an auth token. Once you log in, you can create an API token. It needs to have the “Upload Symbols” permission.

Upload: /upload/

POST /upload/

Upload symbols files as a ZIP file.

Request Headers
  • Content-Type

    the content type of the payload

    • use multipart/form-data for Upload by HTTP POST

    • use application/x-www-form-urlencoded for Upload by Download URL

  • Auth-Token – the value of the auth token you’re using

  • User-Agent – please provide a unique user agent to make it easier for us to help you debug problems

Form Parameters

    the key is the name of the file and the value is the contents of the file; for example symbols.zip=<BINARY>

    Use this for HTTP POST.

    Set this or url–don’t set both.

  • url

    the url for the symbols file

    Use this for Upload by Download URL

    Set this or <FILENAME>–don’t set both.

  • try – use try=1 if this is an upload of try symbols

Status Codes

Symbols processing

Tecken processes ZIP files in a couple of steps.

First, it validates the ZIP file. See section below on “Checks and Validation”.

Once the ZIP file is validated, Tecken uploads the files in the ZIP file. For files that are already in AWS S3, it skips the uploading step and just logs the filename.

Records of the upload and what files were in it are available on the website.


Symbols files can not be overwritten. Once a file is uploaded, any future upload attempts for that debug_filename/debug_id combination will be skipped.

Which S3 Bucket

The S3 bucket that gets used for upload is based on a “default” and a map of exceptions for certain users.

The default is configured as DJANGO_UPLOAD_DEFAULT_URL. For example: https://s3-us-west-2.amazonaws.com/org-mozilla-symbols-public. From the URL the bucket name is deduced and that’s the default S3 bucket used.

The overriding is based on the uploader’s email address. The default configuration is to make no exceptions. But you can set DJANGO_UPLOAD_URL_EXCEPTIONS as a Python dict like this:

$ export DJANGO_UPLOAD_URL_EXCEPTIONS={'*@adobe.com': 'https://s3.amazonaws.com/private-bucket'}

Checks and Validations

First, Tecken checks the ZIP file to see if it’s a valid ZIP file that contains at least one file.

Then, Tecken iterates over the files in the ZIP file and checks if any file contains the list of strings in settings.DISALLOWED_SYMBOLS_SNIPPETS. This check is a block list check to make sure proprietary files are never uploaded in S3 buckets that might be exposed publicly.

To override this amend the DJANGO_DISALLOWED_SYMBOLS_SNIPPETS environment variable as a comma separated list. But be aware to include the existing defaults which can be seen in settings.py.

The final check is to make sure that each file in the ZIP file is either:

  1. <module>/<debug_id>/<file> for symbols files.


  2. <name>-symbols.txt for file listings relative to the root of the zip file.

    While these files can exist in your ZIP file, they’re silently ignored.


Certain files get gzipped before being uploaded into S3. At the time of writing that list is all .sym files. S3, unlike something like Nginx, doesn’t do content encoding on the fly based on the client’s capabilities. Instead, we manually gzip the file in memory in Tecken and set the additional ContentEncoding header to gzip. Since these .sym files are always text based, it saves a lot of memory in the S3 storage.

Additionally, the .sym files get their content type (aka. mime type) set when uploading to S3 to text/plain. Because S3 can’t know in advance that the files are actually ASCII plain text, if you try to open them in a browser it will set the Content-Type to application/octet-stream which makes it hard to quickly look at its content in a browser.

Both the gzip and the mimetype overrides can be changed by setting the DJANGO_COMPRESS_EXTENSIONS and DJANGO_MIME_OVERRIDES environment variables. See settings.py for the current defaults.

Metadata and Optimization

For every gzipped file we upload, we attach 2 pieces of metadata to the key:

  1. Original size

  2. Original MD5 checksum

The reasons for doing this is to be able to quickly skip a file if it’s uploaded a second time.

A similar approach is done for files that don’t need to be compressed. In the case of those files, we skip uploading, again, simply if the file size of an existing file hasn’t changed. However, that approach is too expensive for compressed files. If we don’t store and retrieve the original size and original MD5 checksum, we have to locally compress the file to be able to make that final size comparison. By instead checking the original size (and hash) we can skip early without having to do the compression again.