[RESEND PATCH 08/12] golang/xenlight: add functional options to configure Context

[Nick Rosbrook <rosbrookn@xxxxxxxxx>]

Add a ContextOption type to support functional options in NewContext.
Then, add a variadic ContextOption parameter to NewContext, which allows
callers to specify 0 or more configuration options.

For now, just add the WithLogLevel option so that callers can set the
log level of the Context's xentoollog_logger. Future configuration
options can be created by adding an appropriate field to the
contextOptions struct and creating a With<OptionName> function to return
a ContextOption

Signed-off-by: Nick Rosbrook <rosbrookn@xxxxxxxxxxxx>
---
 tools/golang/xenlight/xenlight.go | 44 +++++++++++++++++++++++++++++--
 1 file changed, 42 insertions(+), 2 deletions(-)

diff --git a/tools/golang/xenlight/xenlight.go 
b/tools/golang/xenlight/xenlight.go
index f68d7b6e97..65f93abe32 100644
--- a/tools/golang/xenlight/xenlight.go
+++ b/tools/golang/xenlight/xenlight.go
@@ -136,7 +136,7 @@ func sigchldHandler(ctx *Context) {
 }
 
 // NewContext returns a new Context.
-func NewContext() (ctx *Context, err error) {
+func NewContext(opts ...ContextOption) (ctx *Context, err error) {
        ctx = &Context{}
 
        defer func() {
@@ -146,8 +146,19 @@ func NewContext() (ctx *Context, err error) {
                }
        }()
 
+       // Set the default context options. These fields may
+       // be modified by the provided opts.
+       copts := &contextOptions{
+               logLevel: LogLevelError,
+       }
+
+       for _, opt := range opts {
+               opt.apply(copts)
+       }
+
        // Create a logger
-       ctx.logger = C.xtl_createlogger_stdiostream(C.stderr, C.XTL_ERROR, 0)
+       ctx.logger = C.xtl_createlogger_stdiostream(C.stderr,
+               C.xentoollog_level(copts.logLevel), 0)
 
        // Allocate a context
        ret := C.libxl_ctx_alloc(&ctx.ctx, C.LIBXL_VERSION, 0,
@@ -201,6 +212,35 @@ func (ctx *Context) Close() error {
        return nil
 }
 
+type contextOptions struct {
+       logLevel LogLevel
+}
+
+// ContextOption is used to configure options for a Context.
+type ContextOption interface {
+       apply(*contextOptions)
+}
+
+type funcContextOption struct {
+       f func(*contextOptions)
+}
+
+func (fco *funcContextOption) apply(c *contextOptions) {
+       fco.f(c)
+}
+
+func newFuncContextOption(f func(*contextOptions)) *funcContextOption {
+       return &funcContextOption{f}
+}
+
+// WithLogLevel sets the log level for a Context's logger. The default level is
+// LogLevelError.
+func WithLogLevel(level LogLevel) ContextOption {
+       return newFuncContextOption(func(co *contextOptions) {
+               co.logLevel = level
+       })
+}
+
 // LogLevel represents an xentoollog_level, and can be used to configre the log
 // level of a Context's logger.
 type LogLevel int
-- 
2.17.1