Initial Functionality

The initial functionality works.  There's still a number of TODOs to
clean up, and some edge cases to work around, and some errors that could
be handled better.

pkg/client/api.go

@@ -0,0 +1,212 @@
+// Copyright 2017 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package prometheus provides bindings to the Prometheus HTTP API:
+// http://prometheus.io/docs/querying/api/
+package client
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/url"
+	"path"
+	"io/ioutil"
+	"io"
+
+	"github.com/prometheus/common/model"
+	"github.com/golang/glog"
+)
+
+// APIClient is a raw client to the Prometheus Query API.
+// It knows how to appropriately deal with generic Prometheus API
+// responses, but does not know the specifics of different endpoints.
+// You can use this to call query endpoints not represented in Client.
+type GenericAPIClient interface {
+	// Do makes a request to the Prometheus HTTP API against a particular endpoint.  Query
+	// parameters should be in `query`, not `endpoint`.  An error will be returned on HTTP
+	// status errors or errors making or unmarshalling the request, as well as when the
+	// response has a Status of ResponseError.
+	Do(ctx context.Context, verb, endpoint string, query url.Values) (APIResponse, error)
+}
+
+// httpAPIClient is a GenericAPIClient implemented in terms of an underlying http.Client.
+type httpAPIClient struct {
+	client *http.Client
+	baseURL *url.URL
+}
+
+func (c *httpAPIClient) Do(ctx context.Context, verb, endpoint string, query url.Values) (APIResponse, error) {
+	u := *c.baseURL
+	u.Path = path.Join(c.baseURL.Path, endpoint)
+	u.RawQuery = query.Encode()
+	req, err := http.NewRequest(verb, u.String(), nil)
+	if err != nil {
+		// TODO: fix this to return Error?
+		return APIResponse{}, fmt.Errorf("error constructing HTTP request to Prometheus: %v", err)
+	}
+	req.WithContext(ctx)
+
+	resp, err := c.client.Do(req)
+	defer func() {
+		if resp != nil {
+			resp.Body.Close()
+		}
+	}()
+
+	if err != nil {
+		return APIResponse{}, err
+	}
+
+	if glog.V(6) {
+		glog.Infof("%s %s %s", verb, u.String(), resp.Status)
+	}
+
+	code := resp.StatusCode
+
+	// codes that aren't 2xx, 400, 422, or 503 won't return JSON objects
+	if code/100 != 2 && code != 400 && code != 422 && code != 503 {
+		return APIResponse{}, &Error{
+			Type: ErrBadResponse,
+			Msg: fmt.Sprintf("unknown response code %d", code),
+		}
+	}
+
+	var body io.Reader = resp.Body
+	if glog.V(8) {
+		data, err := ioutil.ReadAll(body)
+		if err != nil {
+			return APIResponse{}, fmt.Errorf("unable to log response body: %v", err)
+		}
+		glog.Infof("Response Body: %s", string(data))
+		body = bytes.NewReader(data)
+	}
+
+	var res APIResponse
+	if err = json.NewDecoder(body).Decode(&res); err != nil {
+		// TODO: return what the body actually was?
+		return APIResponse{}, &Error{
+			Type: ErrBadResponse,
+			Msg:  err.Error(),
+		}
+	}
+
+	if res.Status == ResponseError {
+		return res, &Error{
+			Type: res.ErrorType,
+			Msg: res.Error,
+		}
+	}
+
+	return res, nil
+}
+
+// NewGenericAPIClient builds a new generic Prometheus API client for the given base URL and HTTP Client.
+func NewGenericAPIClient(client *http.Client, baseURL *url.URL) GenericAPIClient {
+	return &httpAPIClient{
+		client: client,
+		baseURL: baseURL,
+	}
+}
+
+const (
+	queryURL = "/api/v1/query"
+	queryRangeURL = "/api/v1/query_range"
+	seriesURL = "/api/v1/series"
+)
+
+// queryClient is a Client that connects to the Prometheus HTTP API.
+type queryClient struct {
+	api GenericAPIClient
+}
+
+// NewClientForAPI creates a Client for the given generic Prometheus API client.
+func NewClientForAPI(client GenericAPIClient) Client {
+	return &queryClient{
+		api: client,
+	}
+}
+
+// NewClient creates a Client for the given HTTP client and base URL (the location of the Prometheus server).
+func NewClient(client *http.Client, baseURL *url.URL) Client {
+	genericClient := NewGenericAPIClient(client, baseURL)
+	return NewClientForAPI(genericClient)
+}
+
+func (h *queryClient) Series(ctx context.Context, interval model.Interval, selectors ...Selector) ([]Series, error) {
+	vals := url.Values{}
+	if interval.Start != 0 {
+		vals.Set("start", interval.Start.String())
+	}
+	if interval.End != 0 {
+		vals.Set("end", interval.End.String())
+	}
+
+	for _, selector := range selectors {
+		vals.Add("match[]", string(selector))
+	}
+
+	res, err := h.api.Do(ctx, "GET", seriesURL, vals)
+	if err != nil {
+		return nil, err
+	}
+
+	var seriesRes []Series
+	err = json.Unmarshal(res.Data, &seriesRes)
+	return seriesRes, err
+}
+
+func (h *queryClient) Query(ctx context.Context, t model.Time, query Selector) (QueryResult, error) {
+	vals := url.Values{}
+	vals.Set("query", string(query))
+	if t != 0 {
+		vals.Set("time", t.String())
+	}
+	// TODO: get timeout from context...
+
+	res, err := h.api.Do(ctx, "GET", queryURL, vals)
+	if err != nil {
+		return QueryResult{}, err
+	}
+
+	var queryRes QueryResult
+	err = json.Unmarshal(res.Data, &queryRes)
+	return queryRes, err
+}
+
+func (h *queryClient) QueryRange(ctx context.Context, r Range, query Selector) (QueryResult, error) {
+	vals := url.Values{}
+	vals.Set("query", string(query))
+
+	if r.Start != 0 {
+		vals.Set("start", r.Start.String())
+	}
+	if r.End != 0 {
+		vals.Set("end", r.End.String())
+	}
+	if r.Step != 0 {
+		vals.Set("step", model.Duration(r.Step).String())
+	}
+	// TODO: get timeout from context...
+
+	res, err := h.api.Do(ctx, "GET", queryRangeURL, vals)
+	if err != nil {
+		return QueryResult{}, err
+	}
+
+	var queryRes QueryResult
+	err = json.Unmarshal(res.Data, &queryRes)
+	return queryRes, err
+}