Add Span API.

api/include/opentelemetry/trace/canonical_code.h

@@ -0,0 +1,137 @@
+#pragma once
+
+#include <cstdint>
+
+namespace opentelemetry
+{
+namespace trace
+{
+enum class CanonicalCode : uint8_t
+{
+  /**
+   * The operation completed successfully.
+   */
+  OK = 0,
+
+  /**
+   * The operation was cancelled (typically by the caller).
+   */
+  CANCELLED = 1,
+
+  /**
+   * Unknown error. An example of where this error may be returned is if a Status value received
+   * from another address space belongs to an error-space that is not known in this address space.
+   * Also errors raised by APIs that do not return enough error information may be converted to
+   * this error.
+   */
+  UNKNOWN = 2,
+
+  /**
+   * Client specified an invalid argument. Note that this differs from FAILED_PRECONDITION.
+   * INVALID_ARGUMENT indicates arguments that are problematic regardless of the state of the
+   * system (e.g., a malformed file name).
+   */
+  INVALID_ARGUMENT = 3,
+
+  /**
+   * Deadline expired before operation could complete. For operations that change the state of the
+   * system, this error may be returned even if the operation has completed successfully. For
+   * example, a successful response from a server could have been delayed long enough for the
+   * deadline to expire.
+   */
+  DEADLINE_EXCEEDED = 4,
+
+  /**
+   * Some requested entity (e.g., file or directory) was not found.
+   */
+  NOT_FOUND = 5,
+
+  /**
+   * Some entity that we attempted to create (e.g., file or directory) already exists.
+   */
+  ALREADY_EXISTS = 6,
+
+  /**
+   * The caller does not have permission to execute the specified operation. PERMISSION_DENIED
+   * must not be used for rejections caused by exhausting some resource (use RESOURCE_EXHAUSTED
+   * instead for those errors). PERMISSION_DENIED must not be used if the caller cannot be
+   * identified (use UNAUTHENTICATED instead for those errors).
+   */
+  PERMISSION_DENIED = 7,
+
+  /**
+   * Some resource has been exhausted, perhaps a per-user quota, or perhaps the entire file system
+   * is out of space.
+   */
+  RESOURCE_EXHAUSTED = 8,
+
+  /**
+   * Operation was rejected because the system is not in a state required for the operation's
+   * execution. For example, directory to be deleted may be non-empty, an rmdir operation is
+   * applied to a non-directory, etc.
+   *
+   * A litmus test that may help a service implementor in deciding between FAILED_PRECONDITION,
+   * ABORTED, and UNAVAILABLE: (a) Use UNAVAILABLE if the client can retry just the failing call.
+   * (b) Use ABORTED if the client should retry at a higher-level (e.g., restarting a
+   * read-modify-write sequence). (c) Use FAILED_PRECONDITION if the client should not retry until
+   * the system state has been explicitly fixed. E.g., if an "rmdir" fails because the directory
+   * is non-empty, FAILED_PRECONDITION should be returned since the client should not retry unless
+   * they have first fixed up the directory by deleting files from it.
+   */
+  FAILED_PRECONDITION = 9,
+
+  /**
+   * The operation was aborted, typically due to a concurrency issue like sequencer check
+   * failures, transaction aborts, etc.
+   *
+   * See litmus test above for deciding between FAILED_PRECONDITION, ABORTED, and UNAVAILABLE.
+   */
+  ABORTED = 10,
+
+  /**
+   * Operation was attempted past the valid range. E.g., seeking or reading past end of file.
+   *
+   * Unlike INVALID_ARGUMENT, this error indicates a problem that may be fixed if the system
+   * state changes. For example, a 32-bit file system will generate INVALID_ARGUMENT if asked to
+   * read at an offset that is not in the range [0,2^32-1], but it will generate OUT_OF_RANGE if
+   * asked to read from an offset past the current file size.
+   *
+   * There is a fair bit of overlap between FAILED_PRECONDITION and OUT_OF_RANGE. We recommend
+   * using OUT_OF_RANGE (the more specific error) when it applies so that callers who are
+   * iterating through a space can easily look for an OUT_OF_RANGE error to detect when they are
+   * done.
+   */
+  OUT_OF_RANGE = 11,
+
+  /**
+   * Operation is not implemented or not supported/enabled in this service.
+   */
+  UNIMPLEMENTED = 12,
+
+  /**
+   * Internal errors. Means some invariants expected by underlying system has been broken. If you
+   * see one of these errors, something is very broken.
+   */
+  INTERNAL = 13,
+
+  /**
+   * The service is currently unavailable. This is a most likely a transient condition and may be
+   * corrected by retrying with a backoff.
+   *
+   * See litmus test above for deciding between FAILED_PRECONDITION, ABORTED, and UNAVAILABLE.
+   */
+  UNAVAILABLE = 14,
+
+  /**
+   * Unrecoverable data loss or corruption.
+   */
+  DATA_LOSS = 15,
+
+  /**
+   * The request does not have valid authentication credentials for the operation.
+   */
+  UNAUTHENTICATED = 16,
+};
+
+}  // namespace trace
+}  // namespace opentelemetry

api/include/opentelemetry/trace/noop.h

@@ -1,5 +1,12 @@
 #pragma once
+// Please refer to provider.h for documentation on how to obtain a Tracer object.
+//
+// This file is part of the internal implementation of OpenTelemetry. Nothing in this file should be
+// used directly. Please refer to span.h and tracer.h for documentation on these interfaces.
 
+#include "opentelemetry/nostd/string_view.h"
+#include "opentelemetry/nostd/unique_ptr.h"
+#include "opentelemetry/trace/span.h"
 #include "opentelemetry/trace/tracer.h"
 
 #include <memory>
@@ -9,22 +16,34 @@ namespace opentelemetry
 namespace trace
 {
 /**
- * Noop implementation of Span.
+ * No-op implementation of Span. This class should not be used directly.
  */
 class NoopSpan final : public Span
 {
 public:
   explicit NoopSpan(const std::shared_ptr<Tracer> &tracer) noexcept : tracer_{tracer} {}
 
-  // Span
+  void AddEvent(nostd::string_view name) noexcept override {}
+
+  void AddEvent(nostd::string_view name, core::SystemTimestamp timestamp) noexcept override {}
+  void AddEvent(nostd::string_view name, core::SteadyTimestamp timestamp) noexcept override {}
+
+  void SetStatus(CanonicalCode code, nostd::string_view description) noexcept override {}
+
+  void UpdateName(nostd::string_view name) noexcept override {}
+
+  void End() noexcept override {}
+
+  bool IsRecording() const noexcept override { return false; }
+
   Tracer &tracer() const noexcept override { return *tracer_; }
 
 private:
   std::shared_ptr<Tracer> tracer_;
 };
 
 /**
- * Noop implementation of Tracer
+ * No-op implementation of Tracer.
  */
 class NoopTracer final : public Tracer, public std::enable_shared_from_this<NoopTracer>
 {

api/include/opentelemetry/trace/span.h

@@ -1,38 +1,111 @@
 #pragma once
 
+#include <cstdint>
+
 #include "opentelemetry/core/timestamp.h"
+#include "opentelemetry/nostd/string_view.h"
+#include "opentelemetry/trace/canonical_code.h"
 
 namespace opentelemetry
 {
 namespace trace
 {
+enum class SpanKind
+{
+  kInternal,
+  kServer,
+  kClient,
+  kProducer,
+  kConsumer,
+};
 /**
- * StartSpanOptions provides options to set properties of span at the time of starting a new span.
+ * StartSpanOptions provides options to set properties of a Span at the time of its creation
  */
 struct StartSpanOptions
 {
-  // Sets the start time of a span.
+  // Optionally sets the start time of a Span.
   //
-  // If the start time of a span is set, timestamps from both the system clock and steady clock
-  // should be provided.
+  // If the start time of a Span is set, timestamps from both the system clock and steady clock
+  // must be provided.
   //
-  // Timestamps from the steady clock can be used to most accurately measure a span's
-  // duration, while timestamps from the system clock can be used to most accurately place a span's
-  // time point relative to other spans collected across a distributed system.
+  // Timestamps from the steady clock can be used to most accurately measure a Span's
+  // duration, while timestamps from the system clock can be used to most accurately place a Span's
+  // time point relative to other Spans collected across a distributed system.
   core::SystemTimestamp start_system_time;
   core::SteadyTimestamp start_steady_time;
+
+  // TODO:
+  // Span(Context?) parent;
+  // SpanContext remote_parent;
+  // Links
+  // Attributes
+  SpanKind kind = SpanKind::kInternal;
 };
 
 class Tracer;
 
 /**
- * A span represents a single operation within a trace.
+ * A Span represents a single operation within a Trace.
  */
 class Span
 {
 public:
+  // Note that Spans should be created using the Tracer class. Please refer to
+  // tracer.h for documentation.
+  Span() = default;
+
+  // The Span destructor End()s the Span, if it hasn't been ended already.
   virtual ~Span() = default;
 
+  // Not copiable or movable.
+  Span(const Span &) = delete;
+  Span(Span &&)      = delete;
+  Span &operator=(const Span &) = delete;
+  Span &operator=(Span &&) = delete;
+
+  // TODO
+  // Sets an attribute on the Span. If the Span previously contained a mapping for
+  // the key, the old value is replaced.
+  //
+  // If an empty string is used as the value, the attribute will be silently
+  // dropped. Note: this behavior could change in the future.
+  // virtual void SetAttribute(nostd::string_view key, AttributeValue&& value) = 0;
+
+  // Adds an event to the Span.
+  virtual void AddEvent(nostd::string_view name) noexcept = 0;
+
+  // Adds an event to the Span, with a custom timestamp.
+  virtual void AddEvent(nostd::string_view name, core::SystemTimestamp timestamp) noexcept = 0;
+  virtual void AddEvent(nostd::string_view name, core::SteadyTimestamp timestamp) noexcept = 0;
+
+  // TODO
+  // Adds an event to the Span, with a custom timestamp, and attributes.
+  // virtual void AddEvent(nostd::string_view name, core::SteadyTimestamp
+  // timestamp, nostd::span<const std::pair<nostd::string_view name, AttributeValue
+  // value>> attributes) noexcept = 0;
+
+  // Sets the status of the span. The default status is OK. Only the value of the last call will be
+  // recorded, and implementations are free to ignore previous calls.
+  virtual void SetStatus(CanonicalCode code, nostd::string_view description) noexcept = 0;
+
+  // Updates the name of the Span. If used, this will override the name provided
+  // during creation.
+  virtual void UpdateName(nostd::string_view name) noexcept = 0;
+
+  // Mark the end of the Span. Only the timing of the first End call for a given Span will
+  // be recorded, and implementations are free to ignore all further calls.
+  virtual void End() noexcept = 0;
+
+  // TODO
+  // virtual void End(EndSpanOptions&& opts) noexcept = 0;
+
+  // TODO
+  // SpanContext context() const noexcept = 0;
+
+  // Returns true if this Span is recording tracing events (e.g. SetAttribute,
+  // AddEvent).
+  virtual bool IsRecording() const noexcept = 0;
+
   virtual Tracer &tracer() const noexcept = 0;
 };
 }  // namespace trace