rfc(feature): Source context via links (#74)

Author: vaind

README.md

@@ -37,5 +37,6 @@ This repository contains RFCs and DACIs. Lost?
 - [0071-continue-trace-over-process-boundaries](text/0071-continue-trace-over-process-boundaries.md): Continue trace over process boundaries
 - [0072-kafka-schema-registry](text/0072-kafka-schema-registry.md): Kafka Schema Registry
 - [0073-usage-of-transaction-types](text/0073-usage-of-transaction-types.md): Usage of transaction types
+- [0074-source-context-via-links](text/0074-source-context-via-links.md): Source context via links
 - [0078-escalating-issues](text/0078-escalating-issues.md): Escalating Issues
 - [0080-issue-states](text/0080-issue-states.md): Issue States

text/0074-source-context-via-links.md

@@ -0,0 +1,75 @@
+- Start Date: 2023-02-15
+- RFC Type: feature
+- RFC PR: <https://github.com/getsentry/rfcs/pull/74>
+- RFC Status: draft
+
+# Summary
+
+In situations where a source code link and a line number is available for a frame, present the link in the UI and show
+the source code surrounding the line.
+
+# Motivation
+
+The source context is currently composed of three [`Frame` attributes](https://develop.sentry.dev/sdk/event-payloads/stacktrace/#frame-attributes):
+
+- `context_line` - Source code in filename at `lineno`.
+- `pre_context` - A list of source code lines before `context_line` (in order) – usually [`lineno - 5:lineno`].
+- `post_context` - A list of source code lines after `context_line` (in order) – usually [`lineno + 1:lineno + 5`].
+
+Showing a source code context and a link to it (e.g. to GitHub) currently works only if the source code itself is
+available during symbolication, thus the attributes are filled in at that time, or if they were already sent with the event by the SDK.
+
+There are, however, situations where we do have a URL representing the source code contents, but not the contents itself (without downloading it), for example:
+
+- Portable-PDB source-link (.NET, see [this `symbolic` issue](https://github.com/getsentry/symbolic/issues/735))
+- [Debuginfod servers](https://www.mankier.com/8/debuginfod#Webapi-/buildid/BUILDID/source/SOURCE/FILE) (we don’t support these yet)
+- SourceMaps (either embedded sourcesContent or using individual source files)
+- via a repository integration in combination with associated commit
+
+In these cases, the actual source code is not necessary to do symbolication (as opposed to source maps and other types
+of obfuscated source containers) but it is useful for end-user when evaluating the issue in the UI.
+
+## Related GH feature requests
+
+- [Extend stack-trace linking UI](https://github.com/getsentry/sentry/issues/35608)
+- [Support stack trace linking when stack frames do not contain line context.](https://github.com/getsentry/sentry/issues/44015)
+
+# Options Considered
+
+## A | Download the source code during symbolication
+
+One option is to download the source code from its link at the time the event is symbolicated, filling the context-related
+`Frame` attributes for each stacktrace frame, while the event is being processed.
+
+### Pros
+
+- Reuses existing fields (changes only needed in the `Symbolicator`).
+- Sources surrounding the frame line are then stored in the database, enabling [search-by-code](https://github.com/getsentry/sentry/issues/3755).
+- May be possible to do server-side authentication (based on project/org configuration) - this would complicate the solution & caching though, as opposed to only supporting publicly available sources.
+
+### Cons
+
+- Downloads all frame sources even though the event/frame may never be viewed by a user.
+- Adds potentially tens of requests for each symbolicated event that has a source link - as many as there are in the stack trace.
+
+## B | Add a source-link to the `Frame` and let the UI handle it
+
+Another option is to extend `Frame` attributes with a new field, e.g. `source_link` and let UI download the source code
+as needed or just display the link.
+
+### Pros
+
+- No overhead on the server for loading sources in situations where the event/frame wouldn't be shown.
+- Requests to fetch the source code, if any, are made by the user browser, thus avoiding potential quota limits.
+
+### Cons
+
+- Sources not available in the database -> can't [search-by-code](https://github.com/getsentry/sentry/issues/3755).
+- Accessing private sources may be problematic. We could still show the source link, though.
+
+# Selected Option - Combined approach
+
+Because neither option is a clear winner, we went for a combined approach, i.e.
+
+- Add a `source_link` field to the frame.
+- Resolve source context from remote URLs, but only for in-app frames.