Reporting is a central mechanism for sending out-of-band error reports to origins from various other components (e.g. HTTP Public Key Pinning, Interventions, or Content Security Policy could potentially use it).
The parts of it that are exposed to the web platform are specified in the draft spec. This document assumes that you've read that one.
Reporting is implemented as part of the network stack in Chromium, such that it can be used by other parts of the network stack (e.g. HPKP) or by non-browser embedders as well as by Chromium.
Almost all of Reporting lives in //net/reporting; there is a small amount of code in //chrome/browser/net to set up Reporting in profiles and provide a persistent store for reports and endpoints across browser restarts.
//netThe top-level class is the ReportingService. This lives in the URLRequestContext, and provides the high-level operations used by other parts of //net and other components: queueing reports, handling configuration headers, clearing browsing data, and so on.
Within ReportingService lives ReportingContext, which in turn contains the inner workings of Reporting, spread across several classes:
The ReportingCache stores undelivered reports and unexpired endpoint configurations.
The ReportingHeaderParser parses Report-To: headers and updates the Cache accordingly.
The ReportingDeliveryAgent reads reports from the Cache, decides which endpoints to deliver them to, and attempts to do so. It uses a couple of helper classes:
The ReportingUploader does the low-level work of delivering reports: accepts a URL and JSON from the DeliveryAgent, creates a URLRequest, and parses the result.
The ReportingEndpointManager keeps track of which endpoints are in use, and manages exponential backoff (using BackoffEntry) for failing endpoints.
The ReportingGarbageCollector periodically examines the Cache and removes reports that have remained undelivered for too long, or that have failed delivery too many times.
The ReportingSerializer reads the Cache and serializes it into a base::Value for persistent storage (in Chromium, as a pref); it can also deserialize a serialized Value back into the Cache.
The ReportingBrowsingDataRemover examines the Cache upon request and removes browsing data (reports and endpoints) of selected types and origins.
//netIn *ProfileImplIOData*::InitializeInternal, the ReportingService is created and set in the URLRequestContext, where the net stack can use it.
(There is currently no interface to Reporting besides “hop over to the IO thread and poke the ReportingService in your favorite URLRequestContext”, but that should change as various components need to queue reports.)
ChromeReportingDelegate implements ReportingDelegate and plumbs the persistent data interface into prefs. It lives in //chrome/browser/net.