Add a pure-virtual getFilterName() to HTTPSourceFilter

Summary:
NOTE: this is one of two candidate designs, pushed as a draft so it can be
compared against D114801323 (same goal, non-pure virtual with a default). Not
final.

`HTTPMessageFilter` has had `getFilterName()` for a long time, and revproxy
uses it to record which filters a response passed through (the
`var.resp_filter_chain` variable, which ends up in CDN access logs and in TRC).
The coro filter hierarchy has no equivalent, so a coro filter chain cannot be
described at all. This adds the same accessor to `HTTPSourceFilter` and
implements it on every subclass.

It is deliberately pure, so a filter cannot land without a name. That is a
bigger change than it sounds: `HTTPSource` is abstract, but `HTTPSourceFilter`
is not -- it implements all three of `HTTPSource`'s pure virtuals by delegating
to `source_`, which is exactly why subclasses can override only what they want
to intercept. A pure virtual makes `HTTPSourceFilter` abstract for the first
time, so every leaf subclass in the repo has to implement the accessor,
including test fixtures. That is ~55 classes across proxygen, bigcache,
manifold, c2p, crackerjack, edgetee, tgc, otel_gateway, observability query
gateway, sandlet and oil. One site (`CacheFillRequestTest`) constructed
`HTTPSourceFilter` directly as a pass-through and now needs a named subclass to
compile at all.

Filters that have a non-coro counterpart return the same name --
`StripPerHop`, `Decompression`, `ResponseTracing`, `RequestTracing`,
`websocket-proxy` -- so a chain recorded from either handler is comparable. The
rest are named after themselves, and test fixtures take a `Test` prefix. Two
notes: the per-hop stripping filter in `HTTPCoroRevProxyHandler` was an
anonymous `TransformFilter` configured with lambdas and had no type to hang a
name on, so it becomes a named `StripPerHopSourceFilter`; and
`BodyDecompressionFilter` deliberately has no override, since inheriting
`Decompression` from `DecompressionIngressFilter` is the correct answer.

No behavior change -- nothing reads these names until D114778859 on top.

The known cost of the pure form is that generic filters can only be named by
type, so `Transform`, `Visitor` and `CompletionTransform` are uninformative in
a logged chain even though those instances are doing quite specific jobs.

Reviewed By: hanidamlaj

Differential Revision: D114801329

fbshipit-source-id: 1a9b5be2202e2b623f13d111f07a838adb3d2283

Author: Brian Ecker

proxygen/lib/http/coro/HTTPHybridSource.h

@@ -19,6 +19,9 @@ namespace proxygen::coro {
  */
 class HTTPHybridSource : public HTTPSourceFilter {
  public:
+  [[nodiscard]] std::string_view getFilterName() const noexcept override {
+    return "HybridSource";
+  }
   HTTPHybridSource(std::unique_ptr<HTTPMessage> headers, HTTPSource* source)
       : headerEvent_(std::move(headers), !source) {
     if (source) {

proxygen/lib/http/coro/HTTPSourceFilter.h

@@ -10,6 +10,7 @@
 
 #include "proxygen/lib/http/coro/HTTPSource.h"
 #include <folly/logging/xlog.h>
+#include <string_view>
 
 namespace proxygen::coro {
 
@@ -49,6 +50,8 @@ class HTTPSourceFilter : public HTTPSource {
     }
   }
 
+  [[nodiscard]] virtual std::string_view getFilterName() const noexcept = 0;
+
   // HTTPSource overrides
   folly::coro::Task<HTTPHeaderEvent> readHeaderEvent() override {
     return readHeaderEventImpl(/*deleteOnDone=*/true);

proxygen/lib/http/coro/HTTPSourceHolder.h

@@ -16,6 +16,9 @@ namespace proxygen::coro {
 // read, or stopReading is called on the source.
 class HTTPSourceHolder : public HTTPSourceFilter {
  public:
+  [[nodiscard]] std::string_view getFilterName() const noexcept override {
+    return "SourceHolder";
+  }
   HTTPSourceHolder() = default;
 
   /* implicit */ HTTPSourceHolder(HTTPSource* source)

proxygen/lib/http/coro/filters/CompressionFilter.h

@@ -18,6 +18,9 @@ using FilterParams = proxygen::CompressionFilterUtils::FilterParams;
 namespace proxygen::coro {
 class CompressionFilter : public HTTPSourceFilter {
  public:
+  [[nodiscard]] std::string_view getFilterName() const noexcept override {
+    return "Compression";
+  }
   CompressionFilter(HTTPSource* source,
                     std::shared_ptr<folly::Optional<FilterParams>> params)
       : HTTPSourceFilter(source), params_(std::move(params)) {

proxygen/lib/http/coro/filters/DecompressionFilter.h

@@ -22,6 +22,9 @@ namespace proxygen::coro {
  */
 class DecompressionEgressFilter : public MutateFilter {
  public:
+  [[nodiscard]] std::string_view getFilterName() const noexcept override {
+    return "DecompressionEgress";
+  }
   DecompressionEgressFilter(HTTPSource* source = nullptr);
 };
 
@@ -50,6 +53,11 @@ class DecompressionIngressFilter : public HTTPSourceFilter {
   folly::coro::Task<HTTPBodyEvent> readBodyEvent(
       uint32_t max = std::numeric_limits<uint32_t>::max()) override;
 
+  // Matches the non-coro DecompressionFilter's name.
+  [[nodiscard]] std::string_view getFilterName() const noexcept override {
+    return "Decompression";
+  }
+
   static bool compressionSupported(HTTPMessage& msg);
 
  protected:

proxygen/lib/http/coro/filters/HTTPRedirectHandler.h

@@ -63,6 +63,9 @@ class HTTPRedirectHandler {
  private:
   class RequestFilter : public HTTPSourceFilter {
    public:
+    [[nodiscard]] std::string_view getFilterName() const noexcept override {
+      return "RedirectRequest";
+    }
     explicit RequestFilter(HTTPRedirectHandler& handler) : handler_(handler) {
     }
 
@@ -86,6 +89,9 @@ class HTTPRedirectHandler {
 
   class ResponseFilter : public HTTPSourceFilter {
    public:
+    [[nodiscard]] std::string_view getFilterName() const noexcept override {
+      return "RedirectResponse";
+    }
     explicit ResponseFilter(HTTPRedirectHandler& handler) : handler_(handler) {
     }
 

proxygen/lib/http/coro/filters/Logger.h

@@ -158,6 +158,9 @@ class Logger {
 
   class Filter : public HTTPSourceFilter {
    public:
+    [[nodiscard]] std::string_view getFilterName() const noexcept override {
+      return "Logger";
+    }
     enum class Direction { REQUEST, RESPONSE };
     explicit Filter(Direction dir) : direction_(dir) {
       done = folly::coro::makePromiseContract<void>();

proxygen/lib/http/coro/filters/MutateFilter.h

@@ -21,6 +21,9 @@ namespace proxygen::coro {
  */
 class MutateFilter : public HTTPSourceFilter {
  public:
+  [[nodiscard]] std::string_view getFilterName() const noexcept override {
+    return "Mutate";
+  }
   using HeaderMutateFn = std::function<void(HTTPHeaderEvent&)>;
   using BodyMutateFn = std::function<void(HTTPBodyEvent&)>;
 

proxygen/lib/http/coro/filters/RateLimitFilter.h

@@ -20,6 +20,9 @@ namespace proxygen::coro {
  */
 class RateLimitFilter : public HTTPSourceFilter {
  public:
+  [[nodiscard]] std::string_view getFilterName() const noexcept override {
+    return "RateLimit";
+  }
   explicit RateLimitFilter(HTTPSource* source);
   explicit RateLimitFilter(HTTPSource* source,
                            std::chrono::seconds maxDelay,

proxygen/lib/http/coro/filters/RequestContextFilterFactory.cpp

@@ -14,6 +14,9 @@ namespace proxygen::coro {
 namespace {
 class RequestContextFilter : public HTTPSourceFilter {
  public:
+  [[nodiscard]] std::string_view getFilterName() const noexcept override {
+    return "RequestContext";
+  }
   explicit RequestContextFilter(
       std::shared_ptr<folly::RequestContext> context) noexcept
       : context_{std::move(context)} {