Add db-connect, a SQL over HTTPS server

dbconnect/client.go

@@ -0,0 +1,145 @@
+package dbconnect
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/url"
+	"strings"
+	"time"
+	"unicode"
+	"unicode/utf8"
+)
+
+// Client is an interface to talk to any database.
+//
+// Currently, the only implementation is SQLClient, but its structure
+// should be designed to handle a MongoClient or RedisClient in the future.
+type Client interface {
+	Ping(context.Context) error
+	Submit(context.Context, *Command) (interface{}, error)
+}
+
+// NewClient creates a database client based on its URL scheme.
+func NewClient(ctx context.Context, originURL *url.URL) (Client, error) {
+	return NewSQLClient(ctx, originURL)
+}
+
+// Command is a standard, non-vendor format for submitting database commands.
+//
+// When determining the scope of this struct, refer to the following litmus test:
+// Could this (roughly) conform to SQL, Document-based, and Key-value command formats?
+type Command struct {
+	Statement string        `json:"statement"`
+	Arguments Arguments     `json:"arguments,omitempty"`
+	Mode      string        `json:"mode,omitempty"`
+	Isolation string        `json:"isolation,omitempty"`
+	Timeout   time.Duration `json:"timeout,omitempty"`
+}
+
+// Validate enforces the contract of Command: non empty statement (both in length and logic),
+// lowercase mode and isolation, non-zero timeout, and valid Arguments.
+func (cmd *Command) Validate() error {
+	if cmd.Statement == "" {
+		return fmt.Errorf("cannot provide an empty statement")
+	}
+
+	if strings.Map(func(char rune) rune {
+		if char == ';' || unicode.IsSpace(char) {
+			return -1
+		}
+		return char
+	}, cmd.Statement) == "" {
+		return fmt.Errorf("cannot provide a statement with no logic: '%s'", cmd.Statement)
+	}
+
+	cmd.Mode = strings.ToLower(cmd.Mode)
+	cmd.Isolation = strings.ToLower(cmd.Isolation)
+
+	if cmd.Timeout.Nanoseconds() <= 0 {
+		cmd.Timeout = 24 * time.Hour
+	}
+
+	return cmd.Arguments.Validate()
+}
+
+// UnmarshalJSON converts a byte representation of JSON into a Command, which is also validated.
+func (cmd *Command) UnmarshalJSON(data []byte) error {
+	// Alias is required to avoid infinite recursion from the default UnmarshalJSON.
+	type Alias Command
+	alias := &struct {
+		*Alias
+	}{
+		Alias: (*Alias)(cmd),
+	}
+
+	err := json.Unmarshal(data, &alias)
+	if err == nil {
+		err = cmd.Validate()
+	}
+
+	return err
+}
+
+// Arguments is a wrapper for either map-based or array-based Command arguments.
+//
+// Each field is mutually-exclusive and some Client implementations may not
+// support both fields (eg. MySQL does not accept named arguments).
+type Arguments struct {
+	Named      map[string]interface{}
+	Positional []interface{}
+}
+
+// Validate enforces the contract of Arguments: non nil, mutually exclusive, and no empty or reserved keys.
+func (args *Arguments) Validate() error {
+	if args.Named == nil {
+		args.Named = map[string]interface{}{}
+	}
+	if args.Positional == nil {
+		args.Positional = []interface{}{}
+	}
+
+	if len(args.Named) > 0 && len(args.Positional) > 0 {
+		return fmt.Errorf("both named and positional arguments cannot be specified: %+v and %+v", args.Named, args.Positional)
+	}
+
+	for key := range args.Named {
+		if key == "" {
+			return fmt.Errorf("named arguments cannot contain an empty key: %+v", args.Named)
+		}
+		if !utf8.ValidString(key) {
+			return fmt.Errorf("named argument does not conform to UTF-8 encoding: %s", key)
+		}
+		if strings.HasPrefix(key, "_") {
+			return fmt.Errorf("named argument cannot start with a reserved keyword '_': %s", key)
+		}
+		if unicode.IsNumber([]rune(key)[0]) {
+			return fmt.Errorf("named argument cannot start with a number: %s", key)
+		}
+	}
+
+	return nil
+}
+
+// UnmarshalJSON converts a byte representation of JSON into Arguments, which is also validated.
+func (args *Arguments) UnmarshalJSON(data []byte) error {
+	var obj interface{}
+	err := json.Unmarshal(data, &obj)
+	if err != nil {
+		return err
+	}
+
+	named, ok := obj.(map[string]interface{})
+	if ok {
+		args.Named = named
+	} else {
+		positional, ok := obj.([]interface{})
+		if ok {
+			args.Positional = positional
+		} else {
+			return fmt.Errorf("arguments must either be an object {\"0\":\"val\"} or an array [\"val\"]: %s", string(data))
+		}
+	}
+
+	return args.Validate()
+}